An Enquiry Concerning Human Understanding by David Hume

Bertrand Russell famously summarized Hume's contribution to philosophy, saying that he "developed to its logical conclusion the empiricist philosophy of Locke and Berkeley, and by making it self-consistent made it incredible." Hume is remarkable in that he does not shy away from conclusions that might seem unlikely or unreasonable. Ultimately, he concludes that we have no good reason to believe almost everything we believe about the world, but that this is not such a bad thing. Nature helps us to get by where reason lets us down.

Hume is unquestionably an empiricist philosopher, and he strives to bring the rigor of scientific methodology to bear on philosophical reasoning. His distinction between relations of ideas and matters of fact is absolutely crucial in this respect. Anything we can say about the world is a matter of fact, and thus can be justified only through experience and can be denied without contradiction. Relations of ideas can teach us about mathematical truths, but cannot, as some rationalist philosophers would have, teach us about the existence of our selves, an external world, or God.

If we are left with only matters of fact to get us by in the world, however, we find ourselves greatly limited. How can past experience teach me anything about the future? Even to infer without circularity that future experience will resemble past experience requires some principle that cannot be grounded in past experience. Without that principle, our ability to reason according to cause and effect, and thus the greater part of our ability to reason with matters of fact, is sharply curtailed.

We should be careful to note the tone Hume's skepticism takes here, however. Rather than conclude that we cannot know anything about future events or the external world, he concludes that we are not rationally justifiedin believing the things we do. Hume does not deny that we make certain inferences based on causal reasoning, and indeed insists that we would be unable to live if we didn't do so. His point is simply that we are mistaken if we think that these inferences are in any way justified by reason. That is, there are no grounds for certainty or proof of these inferences.

Hume is a naturalist because he suggests that nature, and not reason, leads us to believe the things we do. Habit has taught us that we are safe in making certain inferences and believing certain things, and so we don't normally worry about them too much. We cannot prove that there is a world external to our senses, but it seems to be a relatively safe assumption by which to live. Rather than try to justify our beliefs or identify the truth, Hume seeks simply to explain why we believe what we believe.

The Enquiry is decidedly a book about epistemology and not about metaphysics. That is, Hume is concerned about what and how we know, and not at all about what is actually the case. For instance, he does not deal with the question of whether there actually are necessary connections between events, he simply asserts that we cannot perceive them. Or perhaps more accurately, Hume argues that, because we cannot perceive necessary connections between events, the question of whether or not they actually exist is irrelevant and meaningless.

Hume is an ardent opponent of rationalist metaphysics, which seeks to answer questions such as whether or not God exists, what the nature or matter and soul is, or whether the soul is immortal. The mind, according to Hume, is not a truth-tracking device, and we misuse it if we think it can bring us to metaphysical conclusions. A Humean science of the mind can describe how the mind works and why it reaches the conclusions it does, but it cannot take us beyond the confines of our own, natural, reason.

Hume's stated method is scientific, of careful observation and inference from particular instances to general principles. The drive of scientific inquiry is to dig deeper and deeper so as to uncover a very few, very simple principles that govern all the complexities that we observe. Newton's genius gives us three very simple laws that can explain and predict all physical phenomena. Hume wishes to perform a similar feat for human understanding (the word "understanding" is used by Hume to describe most broadly the several faculties of human reason). The hope is that Hume will derive a similarly small and simple number of principles that can explain and predict the processes of human thought. His method will be to proceed from simple observation of how the mind works and how we use it in everyday life, and to infer from his observations increasingly general principles that govern our understanding until he reaches a bedrock of simplicity and clarity.

In this respect, Hume follows very much in the empiricist vein of philosophy and owes a large debt to “John Locke”. Locke moved against rationalist philosophy, best exemplified by “Descartes”, which relies heavily upon rational intuition. The empiricist tradition asserts that experience, and not reason, should serve as the basis of philosophical reasoning.

The motivation for Hume's project is made apparent in his complaint that the "accurate and abstract" metaphysics that he is pursuing is frequently looked down upon and disdained. The difficulty and counter-intuitive nature of these inquiries often lead to errors that may seem absurd and prejudicial to future generations. Even today, there is a great deal of debate as to whether there has been any real "progress" in philosophy: we may have refined our discussions and dismissed some bad ideas, but in essence we are still mulling over the same problems that concerned Plato and Aristotle. It would not be unreasonable to suggest that we are no nearer a satisfactory and final answer than the ancient Greeks. Hume hopes that scientific observation can uncover the principles that underlie our reasoning so that we can be more immediately aware of faulty logic and more easily guided along the correct path.

Ever since the scientific revolution of Newton, Galileo, and others, science has been held up as a paradigm of fruitful reasoning. In science, there is a carefully defined methodology that precisely details how we can test a theory and determine whether it is right or wrong. Though it is often difficult to determine the right answer, the scientific method usually prevents us from arriving at answers that are far from the mark. Philosophy lacks any such determinate method, and philosophers are continually taking up conflicting views. For instance, Hume's emphasis on observation goes directly against Descartes' rationalism, which disparages observation in favor of pure reason. Hume hopes that his empiricism will open the way for a carefully defined method that will not allow for such disparity amongst philosophers.

Hume also suggests that his work must be epistemically (epistemic: of, relating to, or involving knowledge; cognitive) prior to the new science that he so lauds. The scientific method is a product of careful reasoning, and is thus subject to the laws of human understanding. While science seems to be in far better shape than philosophy, it too can benefit from his work. In this way, Hume differs from his predecessor, Locke. Locke sees himself as laboring on behalf of the new science, clearing away some of the linguistic rubble that might lead to confusion. While Locke humbly sees himself as simply clearing a path for science, Hume believes that his own work must lay the groundwork upon which science can rest. If he can uncover the precise laws that govern our reasoning and inferences, this should help us draw the right conclusions in our scientific investigations.

Hume brings to bear three important distinctions. The first, and most important, is the distinction between ideas and impressions. This distinction is original to Hume and solves a number of difficulties encountered by Locke. A proper discussion of Hume's footnote would take us too far afield, but we should remark that Hume's criticism of Locke is exact and powerful. The distinction between impressions and ideas might seem quite obvious and of no great importance, but Hume is quite clever to identify the full importance of this distinction. An empirical philosophy asserts that all knowledge comes from experience. For Hume, this would suggest that all knowledge comes from impressions, and so ideas are set up as secondary to impressions.

The second distinction, between complex and simple impressions or ideas, helps draw out further the power of the first distinction. A simple impression might be seeing the color red, while a complex impression might be seeing the totality of what I see right now. A simple idea might be the memory of being angry while a complex idea might be the idea of a unicorn (composed of the idea of a horse and the idea of a horn). Complex ideas and impressions are compounded out of the simple ones.

With these first two distinctions, Hume is creating a hierarchy of mental phenomena. Since the complex is compounded out of the simple and ideas are derived from impressions, everything in our mind is based ultimately upon simple impressions. A complex idea is compounded out of several simple ideas, which are in turn derived from several corresponding simple impressions. Hume thus suggests that a term can only be meaningful if it can be connected with an idea that we can associate with some simple impressions. Hume, we should note, is silently implying that every term must be connected with some idea. In the eighteenth century the philosophy of language had not yet flourished, and it was not clear how difficult it might be to determine precisely how words, ideas, and reality link up. Hume's suggestion that all terms can be analyzed into simple impressions anticipates Russell, who argues that we can analyze all terms into simple demonstratives like "this" or "that." Hume's suggestion comprehends a picture of language according to which the words we use are a complex and opaque expression of a simpler underlying language which proper analysis can bring out.

The third distinction is the three laws of association. If the previous two distinctions give us a geography of the mind, describing its different faculties, this distinction gives us a dynamics of the mind, explaining its movement. According to Hume, any given thought is somehow related to adjacent thoughts just as any given movement in the physical world is somehow related to adjacent moving bodies. His three laws of association, then, might be seen as equivalent to Newton's three laws of motion. With them, Hume hopes to have described fully the dynamics of the mind.

There are a number of objections we might want to raise to Hume's distinctions and the way they are introduced, but we will touch on only a few briefly. First, we might ask how strictly we can distinguish between impressions. Hume argues that ideas can be vague, but that impressions are exact and that the boundaries between them are clearly defined. Is the boundary between the impression of a 57" stick and a 58" stick that clearly defined? There is some level of vagueness in our impressions that Hume does not acknowledge. We could also point out that while we are experienced in distinguishing colors, we are not so good with some other sensations. For instance, we often have trouble distinguishing between tastes.

Second, we might object to Hume's implicit philosophy of language. It seems closely linked to the idea that simple impressions are clearly defined and infallible. It is far from clear, however, why it should be desirable or possible to reduce all our language to simple impressions. What, we might ask, is the simple impression from which is derived the word "sake," for example?

Third, we might ask Hume to be clearer in his distinctions. For instance, are dream images impressions or ideas? Most likely they are ideas, since they consist of a mixture of imagination and memory. However, dreams are (arguably) phenomenally indistinguishable from waking experience: we cannot prove that we are dreaming from within a dream. Thus, all our impressions from within a dream are as real to us as we dream them as waking impressions are to us when we experience them.

Dialogues Concerning Natural Religion by David Hume

Hume's skepticism was the result of more than his strong commitment to the Enlightenment ideal of the supremacy of reason; it was also largely the result of his equally strong commitment to the philosophical principles of British Empiricism. Following in the footsteps of George Berkeley, Hume believed that all factual knowledge derives from experience. In contrast to the rationalists, such as Rene Descartes and Nicolas Malebranche (both influential for Hume), who believed that knowledge of matters of fact can be attained through the use of our reasoning faculty, Hume maintained that all matters of fact are established solely on the basis of our experience of the world. (In other words, according to Hume, you cannot just sit in your armchair, think really hard, and expect to come up with any knowledge of matters of fact. In order to arrive at new substantive knowledge, you have to go out into the world and investigate.)

In exploring the possibilities of human knowledge—whether it be scientific knowledge, moral knowledge, or religious knowledge—the relevant question for Hume was always the same: does our experience of the world provide us with enough evidence to draw a rational inference to the relevant conclusions? If experience does provide us with enough evidence, then the relevant beliefs (e.g. religious belief, in the case of the Dialogues) are justified and so rational, and if experience does not provide us with enough evidence, then the relevant beliefs are not justified and so not rational. (The assertion that a claim is rational if and only if it is supported by the evidence is commonly referred to as evidentialism. Both empiricists and rationalists alike believed firmly in evidentialism.)

Hume's commitment to empiricism accounts for the narrow focus of his religious investigation in the Dialogues. It might seem arbitrary, given the variety of arguments for God's existence that were employed in Hume's day, for him to have focused almost exclusively on one such argument, the argument from design. It is true that this particular argument (which claims that the intricate order and beauty of our universe is proof of an intelligent and benevolent designer) was enjoying a particular vogue during this period, largely because it was espoused by Sir Isaac Newton, but there were also other fashionable arguments, such as the ontological argument (which sought to prove God's existence from His very nature) and the cosmological argument (which claimed that God had to exist in order to account for our existence). Hume's focus makes sense when we consider that the argument from design is the only one of the three that seeks to base its conclusions on evidence drawn from experience of the world. Only the argument from design looks to the world and asks, "is there enough evidence here to justify our belief in an infinitely good, wise, and omnipotent God?"

In engaging in his investigation of religious belief, Hume was engaging three types of 18th century thinkers, each of whom is represented by a character in the dialogue. First of all, he discusses sort of man who would believe in the argument from design, the empirical theist. The empirical theist believes that by looking at the world, we can come to knowledge about both the existence and the nature of God. The most famous empirical theist of Hume's day was Sir Isaac Newton, but there were also other prominent defenders of the position such as the Dutch scientist and theologian Bernard Nieuwentyt. The second type of man that Hume discusses in this dialogue is the orthodox Christian or fideist, who believes that because human intellectual resources are too weak to lead us to any certain truths, we should abandon reason and accept truths on faith. Famous fideists include Montaigne and Pascal. Finally, Hume presents the skeptic, who is not wholly satisfied with either of these alternatives.

It is in part a testament to Hume's fair and thorough treatment of all these positions that followers of all three of these philosophical traditions have claimed Hume as their greatest mouthpiece. It is almost certainly the religious skeptics who have the best case for calling Hume one of their own (he incontrovertibly set the model for all later attacks on the rationality of religious belief), but fideists have been nearly as adamant in declaring him the greatest voice defending religious orthodoxy. The German philosopher J.G Hamann, for instance, was convinced that Hume had provided the most cogent argument for fideism by proving that there was no rational evidence for Christianity. He translated the dialogues into German hoping that Immanual Kant would read them and become a serious Christian. The Danish theologian Søren Kierkegaard, the most important Christian fideist of the nineteenth century, was also very impressed by this interpretation of Hume's position.

In Dialogues Concerning Natural Religion Hume explores whether religious belief can be rational. Because Hume is an empiricist (i.e. someone who thinks that all knowledge comes through experience), he thinks that a belief is rational only if it is sufficiently supported by experiential evidence. So the question is really, is there enough evidence in the world to allow us to infer an infinitely good, wise, powerful, perfect God? Hume does not ask whether we can rationally prove that God exists, but rather whether we can rationally come to any conclusions about God's nature. He asserts that the first question is beyond doubt; the latter is initially undecided.

Hume presents three characters, each of whom represent a different position on this issue, engaged in a dialogue together. Demea argues for the position of religious Orthodoxy, and insists that we cannot possibly come to know the nature of God through reason. He believes, in fact, that we cannot ever know the nature of God at all because God's nature is inherently beyond the capacity of human comprehension. Philo, the philosophical skeptic, agrees with Demea that God is incomprehensible and provides the most convincing arguments for this position. Cleanthes argues the position of empirical theism—the position that we can come to know about God by reasoning from the evidence afforded us by nature—against these two opponents.

Cleanthes bases his belief in empirical theism on the argument from design. According to this argument, the complex order and beauty of our universe can only be explained by positing the existence of an intelligent designer, that is, God. The argument is supposed to work by way of analogy (an argument of this form is called an argument by analogy): (1) The world resembles a finely tuned machine. (2) All machines we know of are created by intelligence (human intelligence). (3) Therefore, the world must also be caused by intelligence (divine intelligence). By looking at nature, in other words, we obtain overwhelming evidence that God's intelligence resembles human intelligence (though of course, in much more perfect form). The argument from design is supposed to be the best case that can be made for the claim that religious belief can be rational. By showing that the argument from design fails, Hume hopes to prove that religious belief cannot possibly be based on reason.

Philo the skeptic delivers Hume's objections to the argument from design. In part II he attempts to demonstrate that the argument from design is not even an actual instance of the sort of argument it purports to be, and as such is faulty. The argument from design seems to be an argument by analogy, but it does not work even under this rubric. First, the analogy between machines and the universe is weak at best, and as such any reasoning based on this analogy must also be weak. Second, the universe and a machine are not strictly analogous phenomena because they are not independently existing entities, rather the universe is a whole and a machine is a part of it.

Philo also argues that it is not true that all order we experience is caused by intelligence that we can sense. Some order, such as that found in organic bodies, is caused by generation and vegetation. There is no reason, then, to think that just because the world is ordered, it is necessarily a result of intelligent design. Finally, an inductive argument (that is, an argument that argues for a conclusion based on past evidence), which the argument from design certainly is, requires repeated experience of the phenomena in question (i.e. repeated experience of the cause followed by the effect). However here the relevant cause (God) and effect (the universe) are both wholly unique, so there is no way that we could have such repeated experience of their existences or anything that resembles them.