by Henry Piper (all rights reserved)
Introduction: The Roots of Empiricism
We have considered various metaphysical and epistemological theories, various views, that is, of reality and of knowledge. We started with Plato’s idealism, according to which reality is limited to the realm of Being, wherein are found eternal forms or ideas and mathematical truths, and knowledge consists of the “recollection” of these unchanging truths through the unchanging human soul. Then we considered Aristotle’s view of substance and causation, according to which reality is a synthesis of form and matter, motion and purpose, subject to an evolving process but always guided by some fixed “first principles” and moving always toward some “final cause.” In Descartes we observed a Platonic distrust of the epistemological reliability of the physical senses, leading to a view of the human self as “thinking thing” and a dualist metaphysics consisting of the separation of mind and body, thought and extension, spirit and matter. In Hobbes’s materialism we saw a direct opponent of Plato and a view of human nature as selfish, greedy, violent, anti-social and domineering, apparently consistent with that materialist metaphysics. In Rousseau we saw a pointed rejoinder to Hobbes’s views both of human nature and of the materialist values to which it must be limited. Finally in Berkeley we confronted the perhaps startling claim that physical matter does not exist and that we could not have any knowledge of it even if it did. There are many points of convergence or at least of overlap among these various philosophies, though it is even clearer that there are countless points of direct disagreement; but it should also be clear that each account is at least substantially coherent in itself, and rationally plausible on its own terms, and thus certainly interesting and worthy of serious consideration. Or is it?
In turning to the philosophy of Scottish philosopher David Hume (1711-1776), we are confronted with a challenge to the entire tradition of philosophy as it had theretofore been pursued, for it is Hume’s basic claim that much of what these and innumerable other philosophers have been studying and arguing about, over a period of over 2000 years, is in fact essentially meaningless, empty and vain. In essence, his claim, more specifically, is that most of what had been known as “metaphysics,” which he refers to disdainfully as “an abstruse philosophy,” had been based on supposed knowledge of things that, Hume will argue, are essentially unknowable and, at least by implication, simply not real, and thus that all so-called “metaphysics” is effectively nothing more than empty words and superstition.
The basis of Hume’s claim is rooted in the thought of the English philosophers Locke and Berkeley, who along with Hume are known for their establishment of philosophical empiricism, which is a school of philosophy that emphasizes the sensible experience of physical nature as the proper source and object of all human knowledge. Specifically, we saw in Berkeley (concerning whom we also briefly considered Locke) the assertion that the only reality we can have any direct contact with is mental perception. For Berkeley, as we saw, this leads to the assertion that “esse is percipi,” that the only reality is the spiritual reality of mental perception. Hume agrees in principle with this insight, but he takes it in a substantially different direction.
The Limits of Philosophy
In condemning philosophy that would exceed the boundaries of human knowledge, Hume says, “Here indeed lies the justest and most plausible objection against a considerable part of metaphysics, that they are not properly a science; but arise either from the fruitless efforts of human vanity, which would penetrate into subjects utterly inaccessible to the understanding, or from the craft of popular superstitions, which, being unable to defend themselves on fair ground, raise these encumbering brambles to cover and protect their weaknesses.” Hume, like Descartes before him, is determined to assure accuracy and reliability in his study, which is why Hume dismisses much of metaphysics for being “not properly a science” and for using obscure language and confusing ideas to conceal the intellectual weakness of what it purports to accomplish. Altogether unlike Descartes, however, and unlike any philosopher we have considered, with the crucial exceptions of Berkeley and Hobbes, Hume insists that all philosophical knowledge must be directly traceable to sense impressions; he claims that no ideas are real unless they come from the direct, sensible perception of physical nature. This is why Hume’s philosophy is known as empiricism: he insists that only empirical knowledge, that is, knowledge derived from the sensible experience of the material world, can count as knowledge. This also distinguishes him from Descartes, who insists, as we have seen, that human thought is independent of the physical world, and moreover that some ideas are innate, like the idea of God (Meditation III), and thus generally that human reason operates independently of sense impressions. For Hume, on the contrary, all we have is the sensible experience of physical nature, and all of our knowledge can only have its origin there.
While Hume himself effectively limits himself to epistemological concerns, and does not venture into the metaphysical terrain that he so vociferously condemns, he would seem at least implicitly to have parked himself squarely and unambiguously in the metaphysical-materialist camp of Hobbes: although we may have no direct epistemological access to material objects in themselves (a matter important to our next philosopher, Immanuel Kant), a materialist metaphysics would still seem to follow, as a practical matter, from Hume’s insistence that only empirical knowledge counts as real knowledge, and thus, at least by implication, that only the objects of empirical knowledge, namely material objects, actually exist. Moreover, Hume’s limitation of philosophy to what originates directly in sense experience would effectively spell the end of all metaphysics and seem to reduce philosophy to “handmaiden” of the physical sciences. In the Introduction’s discussion of the difference between science and philosophy, I noted that the observation of the material world is vital to philosophy in general and to metaphysics in particular; however, I noted also that philosophy, among other things, goes beyond the natural, material world to consider the possibility of the supernatural, it goes beyond the ordinary observations of the physical to consider the extraordinary. Hume, however, would deny philosophy this terrain. We might ask here, in passing: is Hume reasonable in asserting that something doesn’t exist just because we cannot directly observe it with our physical senses?
It is important to note that the historical influence of Hume’s philosophy has been great: his fundamental challenge to the very viability of all metaphysical speculation has been instrumental in the genesis and development of a new branch of philosophy, known today as “Anglo-American Analytic philosophy,” which persists in rejecting as meaningless much of the subject matter of previous and ongoing philosophical, especially metaphysical, speculation. In the philosophy of German philosopher Immanuel Kant (1724-1804), however, which we’ll take up in the next chapter, we shall see a direct reply to Hume’s challenge to metaphysics, a reply that, like Hume’s challenge, continues today. Meanwhile, we shall consider the basis of Hume’s empiricism and consider briefly its implications for our understanding of the human self and human freedom.
Matters of Fact and Relations of Ideas
It is Hume’s project to examine human nature with an eye to what it is capable of knowing and so to establish proper limits to philosophy, for it is Hume’s position that if we cannot know something then there is no point in talking about it; according to Hume, to exceed the limits of human understanding by venturing into the “abstruse questions” of metaphysics will only lead us into “superstition…, absurdity and error.” It is thus that Hume’s approach is essentially epistemological, not metaphysical, and his point of departure is the question, what can human beings know? In response, he asserts that “all the objects of human reason may be divided into two kinds, to wit, Relations of Ideas and Matters of Fact and Existence”: for Hume, these are the only things that can be objects of human knowledge, and everything else might as well not exist and indeed, for practical purposes, does not exist (for even if it did we could never know it, much like what Berkeley says about the putative existence of a material world).
Relations of ideas concern only matters of pure reason, like mathematical and geometrical truths:
That the square of the hypotenuse is equal to the square of the two sides, is a proposition, which expresses a relation between these two figures. That three times five is equal to the half of thirty, expresses a relation between these numbers. Propositions of this kind are discoverable by the mere operation of thought, without dependence on what is anywhere existent in the universe.
So relations of ideas involve truths that are “intuitively or demonstratively certain,” as the denial of them would involve a logical contradiction: we cannot reasonably think that 2 and 3 add up to anything but 5, and our knowledge of these relations of ideas is not empirical but a priori, that is, it is not based on sense impressions but is known prior to or independent of sense experience. So far this is completely consistent with metaphysical though going back to Plato. According to Hume, however, it would seem that the ideas themselves on which these a priori relations are based would, on his own terms, have to have their origin in sense impressions of the material world. This, again, is the meaning of empiricism, the philosophical position that all knowledge is based on sense experience.
The relation, for Hume, between the a priori truths of mathematics and the a posteriori ideas we have of the physical world is unclear, but what is clear is that Hume’s empiricism is exclusively concerned with matters of fact, since these have their origin in sensible experience, which is what empiricism limits its inquiries to. Matters of fact consist of the physical realities of the material world, which we can know about through sense impressions: this word “impression” captures the way that the experience of sensing a physical object is a function of the object’s physically impressing itself upon or into our bodies, as when we touch an object it presses against us, or as when we see an object the light that reflects its appearance physically penetrates our eyes (see my discussion of the physicality of sensation in the chapter on Hobbes). The knowledge of a sense impression registers internally in our mind as an idea, which is simply a mental perception of that external sense impression. Thus there are two kinds of perceptions: first there are the immediate impressions that come to us directly through the senses from external matters of fact, and second there are ideas that are retained internally by the mind. Consistent with his insistence on an empirical foundation for all knowledge, according to Hume all ideas come from impressions: “It must be some one impression that gives rise to every real idea,” and “all our ideas… are copies of our impressions.” In other words, if we have an idea of something that cannot be traced to a direct sense impression, then the idea is not real, it is not an idea of any real thing.
By contrast with relations of ideas, our knowledge of matters of fact, which comes to us from external sense impressions, is utterly unlike the indubitable certainty of the pure internal reasoning of mathematics, for “the contrary of every matter of fact is still possible…. That the sun will not rise tomorrow is no less intelligible a proposition, and implies no more contradiction, than the affirmation that it will rise.” In other words, no matter how obvious it may seem to us that certain things happen in the world in a certain orderly way, such as the rising of the sun, we can, in principle, with perfect ease, and without the least logical contradiction, imagine its contrary, such as that the sun will not rise: “what is may not be,” so “the non-existence of any being, without exception, is as clear and distinct an idea as its existence.” Thus even, in fact, though the sun did actually rise this morning (and we cannot go back in time to make a factual change in that), we can perfectly well—and with no logical contradiction—understand that it might not have risen, and we can readily (and with no logical difficulty) imagine a world in which it did not. Why, we must of course ask, do we feel so strongly that the sun must certainly rise tomorrow (and must certainly have risen this morning)?―is it because it cannot logically be otherwise? Clearly this is not the case, for upon due reflection we can easily observe that the sun could fail to rise tomorrow (and could have failed to rise this morning), for there is no logical reason that would absolutely prevent it, and we can even imagine various physical events that could in fact prevent its rising (recall our discussion of this in the chapter on Plato, concerning the realm of becoming).
Associations of Ideas, Especially “The Law” of Cause and Effect
Once we have acquired sense impressions from our actual, physical experience of living in the material world, we gain ideas from those impressions and we can combine and associate those simple ideas in our minds, in various ways, to form complex ideas, and assuming that we reason soundly, using only real ideas derived from actual sense impressions, we can extend our knowledge by using reason to reflect on those ideas. There are three kinds of such associations of ideas, according to Hume, namely “Resemblance, Contiguity in time or place, and Cause or Effect.” Thus we may see that two things resemble, or look like, each other, or that two things often appear together in time or space; most importantly, we may see that two things regularly happen together, one after the other, in such a way as to imply that the first thing is the cause of the second thing.
The relation of cause and effect is the most important, according to Hume, because “All reasonings concerning matters of fact seem to be founded on Cause and Effect. By means of that relation alone we can go beyond the evidence of our memory and senses.” In other words, it is on the basis of the relation of cause and effect that we develop our knowledge of the world, for all knowledge begins with the question of why something is the way it is—in other words, the question of what causes the things we observe to be the way they are: this is why the answer to a “why” question typically begins with “because,” since the word “because,” by its own terms, introduces the cause of something. As I noted in the Introduction, this is what the physical sciences are all about: the so-called “laws of nature” are themselves nothing but assertions of the chain of physical causes that precede physical events, which stand for explanations of why things are the way they are or why things happen the way they do.
What is the nature of this knowledge? We cannot observe any such things as laws or forces underlying the operations of nature, since all we can know, according to Hume, must be based directly on what we can see. What we do see is that certain things happen over and over again, such as when one billiard ball hits another, the second one begins to move. What we see, in Hume’s terms, is the “constant conjoining” of what are in fact two separate events, namely the motion of the first ball and the motion of the second. But because we have in the past constantly observed the motion of the first conjoined to the motion of the second—that is, we constantly see the second ball move following immediately upon the collision of the two—we unthinkingly grow to expect that the motion of the first ball causes the motion of the second, and moreover that there is a “necessary connection” between the two motions such that the second ball must necessarily move upon its being struck by the first. Such a “necessary connection” would be another way of saying that there is some invisible force or law of nature that makes these events happen this way. But note carefully: Hume claims that there is no such “necessary connection” that we can know!
Thus, says Hume, “We fancy, that were we brought, on a sudden, into this world, we could at first have inferred, that one Billiard-ball would communicate motion to another upon impulse; and that we needed not to have waited for the event, in order to pronounce with certainty concerning it.” In other words, we assume that, even if we suddenly came alive, our minds a blank slate lacking any experience at all, and saw that first ball about to hit the second, that we would expect the second ball to move upon impact. “We are apt to imagine, that we could discover these effects by the mere operation of our reason, without experience”; but this assumption is absolutely wrong, insists Hume, for we could imagine innumerable alternative scenarios, none of which would be rationally unthinkable or contradictory. Moreover, “The mind feels no sentiment or inward impression from the succession of objects: Consequently, there is not, in any single, particular instance of cause and effect, anything which can suggest the idea of power, or necessary connection.” In other words, on a single viewing of the motion of the balls, there occurs no inward, rational sentiment or feeling that the second ball will move following impact with the first.
However, such an inward sentiment does develop, over time, as a result of repeated experiences of events like the collision of the two balls, and this is the basis of our “knowledge” of cause and effect, which Hume refers to as an instance of belief. Moreover, the more regular the patterns have been in the past, the more sure we are inclined to feel that they will repeat themselves in the future and thus the more sure our belief. But this “inward sentiment” of belief, it must be stressed, develops not on an a priori basis of pure reason, but has its origin rather in the customary experience of the repeated patterns; in other words, we derive the idea of cause and effect not from reason, but from the experience of observing things like the “constant conjunction” of the motions of the first and second balls, which have happened to appear together time and again, without fail, to the point that we become more and more confident in our belief that they will do so in the future. Consider carefully the term “happen:” by definition, something that “happens” could also not happen—everything that “happens” just happens to happen—in other words, no “happening” is necessary but is, on the contrary, contingent, and we assume, but, Hume argues, we cannot know, that it is contingent on prior happenings. Note that this can easily be confusing: if one event is known to be contingent on a prior event (such as the motions of the second and first balls), then that implies a “necessary connection” between them—that is, it implies that the first event is the cause of the second. Hume’s whole argument, however, is that we cannot know any such “necessary connection” even though—after repeated (“constant”) experiences of two events happening together (“conjunction,” i.e. the motion of the second ball following the motion of the first)—we develop he “habit” of assuming that there is such a connection—of cause and effect—which leads us to assume that the law of cause and effect is true (which is in turn based on the assumption that the future must resemble the past, which we will consider shortly).
All Knowledge, Including the “Law” of Cause and Effect, is Based Not on Reason but on Experience
Hume’s empiricism insists that we are utterly incapable of any direct, or logical (a priori) knowledge of underlying laws and causes to explain the matters of fact we observe with our senses. We naturally tend to assume or even take for granted that there “must be” some cause that makes it necessary—for example, that the sun rise and in general that things in nature, like the movement of the billiard balls, happen according to certain “laws;” however, we cannot observe these causes or laws in themselves. Thus on Hume’s terms, because we cannot observe such laws—that is, we can have no sense impression of them—they cannot be real ideas of real things; they are in essence nothing more than assumptions that we come to believe over time simply because things like the rising of the sun have always appeared in certain ways and according to what feel like—and that we may come to believe to be—some sort of fixed patterns of natural or scientific “laws.”
This sort of belief, founded upon apparently unshakeable feelings or sentiments, is due to the operation of what Hume refers to as custom or habit, which indeed is the basis, according to Hume’s empiricism, of all our knowledge concerning matters of fact in the world. We assume, based on our past experience of things happening in a regular or customary way, that there is some invisible, underlying “power” or “force” or “energy” or “law”—some “springs or principles,” as Hume puts it—causing things always to happen as they do; but Hume asserts that there is neither any a priori, rational basis for this nor any direct a posteriori (empirical) basis for this since we cannot see any laws. On the contrary, the basis that we do have for assumptions is simply experience itself, and more specifically, the experience we have become accustomed to by seeing things happen over and over again in the same ways. Thus, when we observe the movement of the billiard balls, all we actually see is 1) the cue ball moves, 2) the cue ball collides with the 3-ball, 3) the 3-ball moves; we do not see the “cause” or the “force” that we might assume exists to transfer the motion or energy from one ball to another; and—crucial to understand—we only start assuming that there is such a “force” after repeated viewings of the same event (since the first time we see the pool shot we only see it as three, separate events, and we have no reason to believe that they are “necessarily connected,” since all we actually see is that they are “conjoined”—they happen, on this one occasion, to happen together).
Over time, in other words, we tend to conclude, without even being conscious of it, that there “must be” some hidden force or law that dictates the regular movements of nature, that is, that there is what Hume refers to as a law or “necessary connection” between an effect and its cause; but this “must be” is not based on clear, rational thinking, insists Hume, but merely on our habit or customary experience. So our “knowledge” of such “laws” is empirical in origin, since it is based on the regular sense experience of the physical world, but this knowledge is not in any way based on indubitable, a priori reasoning, since whatever we seem to “know,” like tomorrow’s sunrise (or even the sunrise that has already happened), could rationally also not be (or not have been) true. Therefore, because all our experiences, no matter how regular we may have observed them to be (like the constant repetition of the sunrise), can be otherwise than they have always been, we must acknowledge that there is no chance whatever of certainty in our experience of the world.
More fundamentally still, even such a general “idea” as the law of cause and effect itself—that is, the very proposition that “for every effect there must be a cause”—has absolutely no basis in reason; on the contrary, asserts Hume, the law of cause and effect is itself something that we infer based on repeated, or customary, experience. Again, this is the fundamental basis of Hume’s empiricist philosophy—that knowledge is based not on reason but on experience, and that no idea is real unless it derives directly from a sense impression; and we can never see a “cause,” nor see the “necessary connection” that appears to link what appears to be a cause and what appears to be the effect of that cause. So all scientific knowledge is based merely on inferences we make based on repeated experience. The making of such inferences is known as induction, according to which we derive general explanations for what “causes” things to happen as they do; and the reliability of such explanations is based on our ability to use such “knowledge” to make accurate predictions about similar events in the future, since the ability to make such predictions would indicate that we are correct about the underlying “causes.” (An inductive inference must be distinguished from a deductive inference, for deduction refers to the logical process of mathematics, which is based purely on a priori reasoning and thus produces purely rational conclusions that cannot be false such as 2+3=5.)
So an inductive inference, which is the only means to our knowledge of the matters of fact of the world, is in essence an assumption in the sense that there is no purely rational basis for it—such that, as with all matters of fact, its opposite or contrary could rationally be thought. So even so basic a principle as the proposition that every effect must have a cause is no more than an inductive inference which could logically be false; having said that, however, this law of cause and effect, which is the basis for all “knowledge” of matters of fact beyond the perception of immediate impressions, is a highly reliable assumption, since it is based on, and continues to be verified by, extensive and repeated experience. An inference like “the law” of cause and effect, like all sound, scientific judgments, is not a rash assumption made out of pure caprice; rather, it is an assumption for which we can offer firm and reliable, but not absolute, evidence, precisely in the form of repeated experience and experiment. It is thus something that, for Hume, we can reasonably believe, even though we can never rationally know it to be absolutely true or certain (recall the discussion of the fallibility of science in the Introduction).
As disquieting as it may be to accept that there may be no rational basis for a principle so basic as the proposition that there is no effect without a cause—no reason to accept that “like causes produce like effects” nor that there is a “necessary connection” between a “cause” and its “effect”—there is a yet more fundamental assumption underlying all our thinking and observations of such events, which is an easy assumption to overlook since it is so deeply ingrained in human experience; that is the proposition that “the future naturally resembles the past”—in other words, that the way things have happened in the past must necessarily repeat themselves in the future. But what reason do we have for such an assumption?―none whatsoever, argues Hume. Just because things have happened according to regular and predictable patterns in the past, such as the rising of the sun in the east every morning, there is no reason to expect that things will happen similarly in the future. We assume that the future will resemble the past simply because, in the past, the future has resembled the past, but to say that the future will resemble the past because it has in the past is to argue in a circle—just because something has been a certain way tells us nothing a priori about how it will be. The proposition that things will happen in the future according to the patterns we have observed in the past, together with the ideas of cause and effect and necessary connection, are all alike matters of belief based on empirical observation, and have no basis whatever in pure, a priori reason, that is, reason without the benefit of experience.
But Hume then “Resurrects” the “Necessity” of Cause and Effect!
So, Hume has succeeded in destroying the necessity of the law of cause and effect by establishing that it has no a priori foundation and thus can only be assumed based on empirical experience of the past (which can give us no sure insight into the future). But then he makes an abrupt turnaround by recognizing that, on his own terms, it is impossible for us to know anything unless we assume that the law of cause and effect is true; in other words, it is necessary that we accept the law of cause and effect in order to make knowledge possible. It is thus that, perhaps ironically, Hume establishes the law of cause and effect on a new version of “necessity” that, it should be noted, is really a “hypothetical necessity” (and thus no true logical necessity at all). We can appreciate that we have no choice but to do this if we are to make room for the possibility of knowledge, and it is this “no choice” that forces this new “necessity;” but, again, this is in fact merely a hypothetical convenience, effectively, to permit us to function practically: if we are to function in the world—to “know” what we are doing—we must assume that “the future resembles the past” and that “like causes produce like effects.” This is what Hume means when he rejects the strict skepticism of the Greek philosopher Pyrrho (c. 360-270 BC), or the “radical doubt” of Descartes—which would prevent any possibility of error. “Nature is too strong for principle,” says Hume, by which he means that our natural, human habit that causes us to rely on the law of cause and effect cannot in practice be overcome by the logical, philosophical truth that this “law” cannot itself be known.
What Hume is falling back on, in effect, is the practical verity that we all do in fact rely on the law of cause and effect in everything we do—indeed it would be effectively impossible to “know” what to do without that reliance; however, to repeat, it is only “necessary” on the assumption that we desire to do anything (which, experience continually confirms, we do). In other words, if we are to do anything, then we must assume the truth of cause and effect; but that makes cause and effect a hypothetical (if/ then) proposition, not a necessary one. In short, we rely on the law of cause and effect for the same reason that we rely unconsciously on scientific knowledge in all our daily affairs—indeed, these two “reliances” amount to the same thing (refer again to the Introduction on the fallibility of science).
There is No Such Thing as the “Self”
Since all real ideas come from sense impressions, and since all ideas of real things must be traceable to some sense impression, the question arises, what impression do I have of my self? For Hume, the question is easily answered and its consequence easily stated: there is no impression of a “self,” thus it is not a real idea—in other words, strictly speaking, there is no such thing as a “self.”
Having said that, what is it that we mean by the term “self”? We think of it, says Hume, as an entity characterized by both simplicity and identity; that is, we think of it as a single and undivided thing―it is the simple “I”―and it is constantly the same as itself―identical to itself, it is what it is, “I = I,” which is the definition of “identity.”. But as we reflect on this idea of self, argues Hume, we discover that it is neither ever at one with itself nor ever the same as itself. More specifically, my “self” has—that is, “I” have—constantly various “particular perceptions,” and “when I enter most intimately into what I call myself, I always stumble on some particular perception,” to the point that “I can never catch myself at any time without a perception and never can observe anything but the perception.” In short, like the ideas of cause and effect and necessary connection, this notion of self refers, in itself, to nothing at all; rather, when I use the term “self,” it refers only to some sort of accumulation of experiences that together, with the crucial assistance of memory, serve to make up this idea of self. But all I really have to observe, that is, the only impressions I have in making up this idea of “self” over time, are perceptions—those impressions of external sensation and the internal associations I make of those impressions known as ideas. Thus, says Hume, in essence the self is “nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity and are in a perpetual flux and movement.” And consider what a “bundle” really is: if we have a “bundle of sticks,” and we remove sticks, one by one, from the “bundle,” at some point we are going to be left with just three sticks, then two and then just one—so what happened to the “bundle?” Clearly, there is no such thing as a bundle, in itself, there were only some sticks!
Thus “the mind is a kind of theater where several perceptions successively make their appearance, pass, repass, glide away and mingle in an infinite variety of postures and situations.” But Hume is quick to add that it is not as if this “theater” is any kind of fixed identity, for there is, strictly speaking, no “theater” in itself, rather it is “the successive perceptions only that constitute the mind.” That is, there is nothing but the perceptions, lacking which the self ceases to exist: “When my perceptions are removed for any time, as by sound sleep, so long am I insensible of myself and may truly be said not to exist.” In short, rather than having some personal identity, it is in fact the case that the idea of the self is the exact opposite of “identity”; it is, rather, constituted by a diversity of different, perhaps somehow related, perceptions. In other words, rather than being the same thing, I am exactly the opposite of that, namely a constantly different thing, or rather no “thing” at all but a succession of diverse and distinct perceptions of other things. The idea that my self somehow resides or has its origin in some “soul” or “self” or “substance” is a fiction, according to Hume, something I merely make up or imagine based on some observed relation among various distinct perceptions.
How the Self is Made
Hume considers several models of how we ascribe identity to things that are in fact simply “a succession of related objects,” and thus how we tend to obscure the narrow meaning of the very concept of identity, for it is by not sufficiently understanding this concept that we tend mistakenly to attribute personal identity to our own selves. Hume seems to echo Aristotle’s four causes, material, final, formal and efficient, which for Aristotle are precisely the causes of what make a thing the thing that it is, as he considers the identity of a material object—identity in terms of end or purpose, identity that consists in the form of a thing, then identity in terms of what effects it or brings it about. As for material identity, Hume observes that, strictly speaking, a physical mass only remains identical if there is no change in the material particles of which it consists; however, where an alteration in the mass of a thing is slight, or occurs “gradually and insensibly,” we tend, if mistakenly, to view the mass as the “same thing.” Thus we might consider a sandy beach: if we take a pail of sand away with us when we leave, do we leave the same beach that we found? Strictly speaking, of course, the answer is no, but it would take a lot of visits to the beach, and a lot of missing pails of sand, before we would say that the beach is no longer the same, though assuredly this would eventually happen, indeed, ultimately there would be no beach left at all!
We also mistakenly attribute identity to artificial things like Hume’s example of a ship, that have the same purpose over time yet are changed in their matter; thus, even after repair and replacement of parts we would presumably call it “the same ship” though assuredly it would not in fact be materially identical. We attribute identity to a changing thing also in the case of natural things like “animals and vegetables,” says Hume, “where not only the several parts have a reference to some general purpose, but also a mutual dependence on and connection with each other.” Indeed, continues Hume, “The effect of so strong a relation is that though everyone must allow that in a few years both vegetables and animals endure a total change, yet we still attribute identity to them, while their form, size and substance are entirely altered.”
We also attribute identity to a thing if it remains over time the same kind of thing even if it is not in fact a single, unitary thing; this, observes Hume, is a result of confounding numerical identity (something remaining one and the same unitary thing) and specific identity (something being the same kind of thing as another thing, having, we might say, the same “form”). Hume seems to be suggesting that the narrow sense of identity should technically be limited to numerical identity―to things that are the same as themselves, and so distinct from all other things; but our use of the term “identity” is often lazy and ambiguous. Thus, says Hume, we might say of “a noise that is frequently interrupted and renewed” that “it is still the same noise, though it is evident the sounds have only a specific identity or resemblance and there is nothing numerically the same but the cause which produced [“effected”] them.”
Memory as the Agent of the Self
Having reviewed these various ways that we loosely and indeed mistakenly attribute identity to things that do not in fact remain numerically the same or identical to themselves, Hume turns to personal identity to conclude, “The identity which we ascribe to the mind of man is only a fictitious one and of a like kind with that which we ascribe to vegetables and animal bodies.” This then brings us to the question of what is responsible for, or what is the agent of, the fiction, and Hume’s answer is the memory.
At the beginning of his consideration of the self, as we noted, Hume asserts that there is no real idea of a self, because all ideas come from sense impressions and there is no object of self to have a sense impression of: we can never set eyes on our self. Therefore we are left to explain the idea of the self as a matter not of a real and self-subsistent object but of associations of ideas that are real, namely the perceptions in the mind that have come from sense impressions (recall that perceptions include both impressions and ideas, the former being external, the latter internal); it is thus that Hume describes the self as “a bundle of perceptions.” So the question now is, how do certain perceptions get bundled together in the first place to make up what I refer to as “myself”? Recall that there are three ways that ideas become associated―resemblance, contiguity and cause and effect. Since these are the only three ways that ideas become associated, it can only be by such means that my perceptions become related to one another and so “bundled” into a “self”; and Hume argues that both resemblance and cause and effect, but not contiguity, are at play in so constituting personal identity.
Clearly as I walk along the street, I experience a constant stream of distinct impressions, and it is not difficult to see that each distinct impression I see, from moment to moment, is typically very similar to the ones preceding it, which linger in my memory, since after all it appears to be “same” street I am walking down as I go along. Thus it is easy to see how the mind might string together these succeeding perceptions and attribute them to being the perceptions made by the selfsame object, namely “I,” thus the idea of personal identity, as the “I” who is experiencing this stream of similar perceptions. Thus “the memory not only discovers the identity, but also contributes to its production by producing the relation of resemblance among the perceptions.” (We might note that there may be an objection to this: since the street that I walk along only appears to be the same (but is in fact changing along with each succeeding impression of it), we might wonder how we can be sure that we will automatically recognize this street as the “same” from moment to moment, since it is not in fact the same.)
Thus resemblance seems possibly to account for the mechanical creation of personal identity: I can see how the resemblance of the perceptions of my regular surroundings might naturally lend themselves to a common construction I call my “self.” But more interesting is the operation of cause and effect, concerning which Hume observes that “the true idea of the human mind is to consider it as a system of different perceptions or different existences which are linked together by the relation of cause and effect, and mutually produce, destroy, influence, and modify each other…. In this respect,” says Hume,
I cannot compare the soul more properly to anything than to a republic or a commonwealth in which the several members are united by reciprocal ties of government and subordination and give rise to other persons who propagate the same republic in the incessant changes of its parts. And as the same individual republic may not only change its members, but also its laws and constitutions, in like manner the same person may vary his character and disposition as well as his impressions and ideas without losing his identity. Whatever changes he endures, his several parts are still connected by the relation of causation.
So here again it is the memory, by “showing us the relation of cause and effect among our different perceptions,” that might be responsible for our idea of personal identity. Moreover, because memory makes us aware of “that chain of causes and effects which constitute our self or person,” memory is responsible also for extending the idea of the self even to past events “which we have entirely forgotten, but suppose in general to have existed.” This demonstrates and is a reminder of the importance of the relation of cause and effect, for it is this relation that permits us to infer that such forgotten events must belong to our selves, since it is precisely such events which have evidently caused our present circumstances. Thus Hume can say that “memory does not so much produce as discover personal identity,” implying that there is in fact a personal identity after all, albeit one that experience was required to “discover.”
Finally we might note that I can have the experience that leads to such empirical knowledge only insofar as I am in some sense a coherent being, persisting through time and retaining in memory the record of that persistence. Just as Hume first tears down the idea of the necessity of cause and effect only to “resurrect” it on a new foundation, so he denies the reality of the idea of the self only to rescue a new understanding of personal identity from the vagaries of our understanding of the concept of identity generally. After all, my knowledge of nature presupposes in some sense my knowledge of myself, for it is my knowledge that I seek, and, since Hume discovers and justifies the existence of the self on the same basis on which he discovers and justifies his knowledge of nature, that self can only be bound by the same (hypothetical) “necessity” that makes all knowledge possible. It is thus that, for Hume, the actions of the self must be (presumed to be) bound by the same ironclad certainty of necessity as are the motions of all other natural objects, and this leads to his claim, which we shall turn to now, that there is no essential distinction between human liberty and necessity, which amounts to a denial of the freedom of the will.
There is No Such Thing as “Free Will”
Having founded knowledge upon the ground of belief, based on the observation of the constant conjunction of events, Hume can say, “It is universally allowed that matter, in all its operations, is actuated by a necessary force, and that every natural effect is so precisely determined by the energy of its cause, that no other effect, in such particular circumstances, could possibly have resulted from it.” And Hume claims that we can observe a uniformity in the actions of human beings essentially analogous to the uniformity we observe in the movements of natural bodies. So Hume can say of human beings essentially what he says of material bodies: “it is universally acknowledged, that there is a great uniformity among the actions of men, in all nations and ages, and that human nature remains still the same, in its principles and operations. The same motives always produce the same actions: The same events follow from the same causes.”
The study of history, says Hume, informs us of “the regular springs of human action and behavior,” so that “we mount up to the knowledge of men’s inclinations and motives, from their actions, expressions and even gestures; and again, descend to the interpretations of their actions from our knowledge of their motives and inclinations.” In other words, we gain a general knowledge of the necessary laws that govern human behavior based on observing particular human actions over time, and having developed our knowledge of such “springs and actions of human action and behavior,” we can infer what internal motives and inclinations cause people to do what they do. It is thus that Hume’s views, as I noted above, are consistent with Hobbes’s materialist metaphysics, for we see in Hobbes’s discussion of “the interior beginnings of voluntary motions” a description of precisely the sort of “regular springs of human action” that Hume is here referring to.
When we fail accurately to predict or explain a particular event, whether a natural occurrence or a human action, the failure is attributable simply to our ignorance of all of the causes at work in a particular case, since “almost in every part of nature, there is contained a vast variety of springs and principles, which are hid, by reason of their minuteness or remoteness,” thus where we observe an unexpected or surprising event in nature or human action it can only be the result of “the secret operation of contrary causes,” circumstances, that is, of which we are ignorant and that serve to hinder or alter the ordinary causes with which we are familiar. In principle, therefore, there are no people whose actions cannot be explained and predicted, that is, “accounted for by those, who know every particular circumstance of their character and situation.” So Hume can conclude, “Thus it appears… that the conjunction between motives and voluntary actions is as regular and uniform, as that between the cause and the effect of any part of nature.”
In short, the term “liberty,” according to Hume, is simply that species of natural necessity that we use to refer to the actions of human beings: all the actions of human beings are determined by precisely the same natural necessity of cause and effect as determines the motions of billiard balls. The only difference is that in the case of human “liberty,” the source of the determining cause is to be found in the internal will, not in some external force, as when a ball at rest is impacted from outside by a moving ball: “By liberty then, we can only mean, a power of acting or not acting, according to the determinations of the will; that is, if we choose to remain at rest, we may; if we choose to move, we also may. Now this hypothetical liberty is universally allowed to belong to everyone, who is not a prisoner, and in chains.” In other words, as long as we are not bound by some external constraint, like a prisoner in chains, and thus prevented from having our actions determined by our internal will, we have “liberty,” though the will itself is determined in its choice by the same laws of causal necessity as motivate billiard balls and all material objects. Thus the will itself is no more “free” than those same billiard balls: the will determines what it determines based on the necessity consisting of those “regular springs of human action” that combine to form the “characters” and “inclinations” that form the necessary causes that determine our wills.
Why are we apt to feel that our wills themselves are free? Hume explains that we never pause to question the natural necessity of cause and effect, the necessity, that is, that governs material objects; through the regular observation of constant conjunction, human beings grow so accustomed to the regular patterns of nature as to believe that “they penetrate farther into the powers of nature, and perceive something like the necessary connection between the cause and the effect.” This is an illusion, of course, for Hume has explained how can see nothing of the sort, but our experience of the material world through external sensation is so vivid and regular as to convince us otherwise. As for the observation of internal states, however, human beings do not observe the force of natural necessity at work there: “When again they turn their reflection toward the operation of their own minds, and feel no such connection of the motive and the action; they are thence apt to suppose, that there is a difference between the effects, which result from material force, and those which arise from thought and intelligence.” In other words, we fancy, simply from ignorance and for no reason whatever, that there is no necessity at work in our minds connecting the motive cause to our chosen actions, and thus that there is a difference in what motivates our wills and what simply necessitates the actions of material bodies like billiard balls. But this is false, says Hume: there are precisely the same forces at work in both cases, and the actions of a person at “liberty” are none the less necessary than those of the billiard balls.
That Morality and Punishment are Still Effective Despite Our Having No Free Will
It would seem that Hume’s rejection of the freedom of the will to determine itself would render morality impossible or meaningless, and that it would serve no reasonable purpose to praise “good” actions and to blame and punish “bad” ones, since, without free will, it would seem that a person could not reasonably be responsible for her actions. Hume, however, takes exactly the contrary view, insisting that his views of liberty and necessity “are not only consistent with morality, but are absolutely essential to its support.”
“Actions are,” says Hume, “by their very nature, temporary and perishing; and where they proceed not from some cause in the character and disposition of the person who performed them, they can neither redound to his honor, if good, nor infamy, if evil.” In other words, argues Hume, it only makes sense to hold someone responsible for an action if we can trace that action to some necessary cause that exists within the person, for if there were no such fixed, necessary cause determining the person’s action, we would have no reason to infer that the action was anything other than a fleeting, accidental, one-time thing, and thus no reason to expect that the person would do such a thing again. The will, which is a cause, must still be necessarily connected to the action, which is the will’s effect; moreover, the will cannot be at liberty to will what it will, for if it were then its “temporary and perishing” actions could not reasonably be attributed to any fixed cause operating still within the person. In such a case, blame or punishment would serve no purpose, in the case of a bad action, nor would praise be deserved, in the case of a good one.
Thus, Hume continues, to deny that our actions are the result of necessary causes operating within us would amount to asserting that “a man is as pure and untainted, after having committed the most horrid crime, as at the first moment of his birth.” Thus we can only reasonably judge a person or action as “criminal” if we can trace that action to some necessary cause, present within the person, which thus remains after the action is completed. It is by assuming that there is some such necessary cause still present in the person that we have something to blame and punish, and it is this cause still present in the person that we hope to alter by our blame and punishment. The same reasoning applies here as when we insist that a person must be at “liberty” if we are reasonably to hold the person responsible for an action, since if the action is caused by some external force, this would mean that there would be nothing in the person to blame. In sum, according to Hume, moral judgments of approbation and blame depend on the presence of liberty, that is, on the determination of our actions by the will; however, for morality to make any sense, according to Hume, that “liberty” cannot permit a genuinely free will, for in that case the will would not be the sort of concrete, necessary cause that would justify praise or blame.
Conclusion: How Hume Purports to Rescue Knowledge from Total Skepticism
We have seen how Hume’s extreme empiricism takes him to the brink of a radical skepticism that would seem to eliminate any possibility of knowledge. This is so because, on his own terms, all knowledge is empirical, that is, it can come only from experience, and it relies on the ideas of cause and effect and necessary connection to determine why things are as they are, which in turn rely only on our observation of the “constant conjunction” of events like the successive motions of the two billiard balls. Moreover, there is a yet more fundamental assumption on which all of this relies, an assumption we so take for granted that it is the easiest to overlook, namely that the future will resemble the past; and because there is no logical reason that can foretell the future, and thus no rational justification for a necessary causal connection among our impressions, if we rest in the total skepticism that such doubt entails we would be driven to the conclusion of Berkeley that there is no external, material world. And this same reasoning, we have seen, seems to eliminate the idea of the self, since, according again to Hume’s empiricism, the idea of the self cannot be traced to any sense impression.
However, Hume pulls himself back from the brink of such absolute skepticism, and from the elimination of the self, by relying on the observations of constant conjunctions among perceptions, retained as memories in the mind. It is on the basis of our mental associations of ideas, over time, that we can settle on certain beliefs, such as that the second billiard ball will move upon impact with the first; and it is precisely such beliefs which constitute knowledge itself (which, again, is strictly empirical). Such beliefs have their origin in feelings or sentiments which seem, based on the regularity of our observations, to be inescapably “true,” though it can only be an a posteriori “truth,” that is, derived from experience, rather than the purely rational, a priori truth such as we have in mathematics; and our knowledge can never be absolutely true or certain.
So we presumably can and do infer that there is such a thing as an actual “law” of cause and effect, and such inference is reasonable as long as we recall that it is not an original truth of reason but an artifice that we build up on the basis of constant and repeated experience; moreover, such a “law” counts as scientific “knowledge” only insofar as we can infer that the motion of that second ball is actually caused by the first and thus necessary, for there can be no such thing as “chance” in nature, according to Hume, if we are to be confident in our knowledge of nature. We use the word “chance” simply to indicate our ignorance of the necessary causes behind all the operations of nature (and behind also the operations of each of us); indeed, the word chance is actually meaningless: nothing in nature happens by chance, according to Hume, since everything must operate according to necessary causes if anything is to happen at all, even though we frequently do not know all the causes at work and thus are surprised or mistaken about what happens.
So, “abstruse” as his reasoning may at times appear, Hume seems to flip from the radical empiricism that would eliminate a priori reason as the basis for any knowledge of any matters of fact, to a new basis of knowledge founded, a posteriori, upon belief; and Hume insists that this new basis of knowledge provides a firm foundation for our belief, if nothing more, in the necessity of the connection between cause and effect, a necessity that extends to all of nature including all the actions of human beings. In other words, while Hume begins by undermining any possibility of knowing anything, he ends, ironically, with an insistence on the very necessity of things that he was initially intent to repudiate.
Toward the Philosophy of Kant
Is Hume too quick to assume that there is nothing prior to experience, and thus that no a priori knowledge of matters of fact is possible? He doesn’t hesitate to affirm that “relations of ideas” such as mathematical truths are known a priori, and we, who are otherwise nothing without experience, nonetheless know them; how then can it be that such a priori truths tell us nothing about the world, how can the world of the a priori be so estranged from the world of experience? If we do not merely “produce” our “self,” but also “discover” it, as Hume indicates, then doesn’t that imply that it was somehow before we discovered it? And is Hume correct to insist, with Hobbes, that liberty is simply a kind of necessity, operating according to the same laws that govern all other natural objects, and thus that there is no fully spontaneous power of free will, and are we convinced that morality makes any sense on these terms?
We must turn to Immanuel Kant for a response to these questions.
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