Review: David Hume’s “A Treatise of Human Nature”

by Miles Raymer


David Hume’s A Treatise of Human Nature is not a breezy book. From the first page, it plunged me into a fervid mode of double-layered analysis in which my struggle to comprehend the text was mirrored by efforts to track my personal reactions to whatever content I was able to wrest from it. Early on, my attempts felt futile––understanding occluded by my intellectual limitations and relative lack of outside support. My experience improved as I pressed on, however. Slowly, mysteriously, sentences and paragraphs began congealing into coherent expressions. From time to time, the text would open to me like an unfurling flower, or an exquisite sunrise glimpsed after an unreasonably early tumble out of bed.

Eventually, I came to a predictable conclusion: David Hume was brilliant.

His brilliance is easy to miss, though, especially for a modern reader. Despite the fact that science has validated many of Hume’s core ideas, there are still lots of barriers that make it difficult for a 21st-century mind to grok Hume’s 18th-century philosophy. The most confounding of these barriers are Hume’s Baroque style and his outdated methods of inquiry.

Hume was a product of the late Baroque period, so clarity and brevity were absent from his intellectual toolkit. This text is rife with rambling repetition, and generally conforms to the taxonomic model of philosophy, wherein the author lays out a massive network of terms and provides definitions of varying consistency for each. Hume’s arguments are generally difficult to suss out in the moment, even if they come together after many paragraphs and pages. This can make it tough to fruitfully compare passages from different sections of the text.

Hume’s writing often gives the impression that he’s trying to do a chemistry experiment, or math problem, using inherently fuzzy terms:

Ideas never admit of a total union, but are endow’d with a kind of impenetrability, by which they exclude each other, and are capable of forming a compound by their conjunction, not by their mixture. On the other hand, impressions and passions are susceptible of an entire union; and like colours, may be blended so perfectly together, that each of them may lose itself, and contribute only to vary that uniform impression, which arises from the whole. (260)

This passage is easy enough to grasp if read carefully, but it also brings up questions that admit no satisfactory answer, like “why can impressions and passions be mixed, but ideas can’t?” and “what’s the significant difference between ‘compound’ and ‘mixture’ here?” We have to shrug and concede, Well, that’s just how Hume’s system works. His conceptual system is peculiar to his way of seeing the world, which makes it at least somewhat arbitrary; it can’t be submitted for verification against any objective standard (or it couldn’t in Hume’s day, because no such standard(s) existed). This doesn’t mean Hume is right or wrong about anything in particular, but it does mean we have to accept certain insupportable assertions if we want a shot at hearing him out. The good news is that, ultimately, his message is well worth a listen.

The other big obstacle is the radical difference between “empiricism” as it was understood in the 18th-century and “empiricism” as we use it today. Modern empirical analysis is characterized by data-based scientific inquiry, or other forms of externally-directed information gathering when tackling topics that defy quantification. In Hume’s day, being an empiricist simply meant using your natural sense perceptions as the foundation for trying to gain knowledge of the world, rather than building some abstract conceptual system and trying to cram the world into your prefigured notions of it. Seems obvious today, but back then it was a huge shift in philosophical thought.

The way this cashes out is that A Treatise of Human Nature is full of thought experiments masquerading as empirical knowledge. These “experiments” passed muster in Hume’s time, but would never be treated as “empirical findings” today. So while Hume is certainly a step up from the non-empiricists that came before him, he still anchors a lot of his arguments using imagined results of imagined scenarios. Additionally, he was trying to explain perception and morality long before neuroscience, psychology, or evolutionary theory. Given these enormous handicaps, it’s amazing he got as much right as he did.

And oh, he did! This maw of verbal detritus contains insights that were novel to 18th-century readers, some of which represent mysteries still unsolved by modern philosophy and science. The first of these is a genuine skepticism. Unlike many of his dogmatic predecessors, Hume is comfortable admitting when he doesn’t know something. In fact, he thinks admitting that we don’t know (and perhaps can’t know) certain things is a critical part of inquiry.

Hume develops his skeptical outlook primarily through a series of discursive critiques of how humans perceive cause-and-effect relationships. I found his skepticism most enlightening, however, when applied to his thoughts on personal identity. Toward the end of Book I, he identifies a question that still baffles academics and researchers today: How does the human brain/body construct a consistent notion of personal identity from memories and sense perceptions?

How few of our past actions are there of which we have any memory? Who can tell me, for instance, what were his thoughts and actions on the first of January 1715, the 11th of March 1719, and the 3rd of August 1733? Or will he affirm, because he has entirely forgot the incidents of these days, that the present self is not the same person with the self of that time; and by that means overturn all the most establish’d notions of personal identity? In this view, therefore, memory does not so much produce as discover personal identity, by shewing us the relation of cause and effect among our different perceptions…Identity depends on the relations of ideas; and these relations produce identity, by means of that easy transition they occasion. But as the relations, and the easiness of the transition may diminish by insensible degrees, we have no just standard, by which we can decide any dispute concerning the time, when they acquire or lose a title to the name of identity. All the disputes concerning the identity of connected objects are merely verbal, except so far as the relation of parts gives rise to some fiction or imaginary principle of union. (187, emphasis his)

Without a shred of hard data, Hume understood that personal identity is nothing more than an “imaginary principle of union” generated by the brain’s ability to simulate an “easy transition” between disparate perceptions and memories. Even more remarkable is his willingness to admit that he can’t think of a suitable way to resolve the tension between our feeling of being unified beings and the reality that we’re anything but:

When I enter most intimately into what I call myself, I always stumble on some particular perception or other…I never catch myself at any time without a perception, and never can observe anything but the perception. When my perceptions are remov’d for any time, as by sound sleep; so long am I insensible of myself, and may truly be said not to exist. And were all my perceptions remov’d by death, and cou’d neither think, nor feel, nor see, nor love, nor hate after the dissolution of my body, I shou’d be entirely annihilated, nor do I conceive what is farther requisite to make me a perfect non-entity. If any one, upon serious and unprejudic’d reflexion thinks he has a different notion of himself, I must confess I can reason no longer with him…He may, perhaps, perceive something simple and continu’d, which he calls himself; tho’ I am certain there is no such principle in me. (180, emphasis his)

Hume doesn’t invent some baseless explanation for why human identity isn’t paradoxical, or claim that identity is the product of some metaphysical substance (soul). Nor does he turn to religious solutions (all things are possible…because God!). He runs into a difficult problem, scopes it out as best he can, admits his failure to provide a solution, and contents himself with confronting the mystery. This mixture of brilliance and humility is hard to come by even today, when these matters are much better understood (even if the paradox of identity remains as churlish as ever).

Hume was also ahead of the curve in his evaluation of free will, which he correctly identifies as nothing more than our internal feeling of freedom: “By the will, I mean nothing but the internal impression we feel and are conscious of, when we knowingly give rise to any new motion of our body, or new perception of our mind” (284, emphasis his). That Hume does not seek to exempt the will from the constraints of a strictly causal universe again situates him closer to modern thinkers than those of his own time.

Since Hume saw humans as part of the natural world rather than an exception to it, it may come as no surprise that he locates human emotion and intelligence on a continuum with animals. This position could be a direct (or indirect) reaction to 17th-century biologists who dissected un-anesthetized dogs for experimentation despite the subject’s obvious anguish. Hume encouraged the reader to “take a general survey of the universe, and observe the force of sympathy thro’ the whole animal creation, and the easy communication of sentiments from one thinking being to another” (258). This attitude no doubt helped pave the way for the philosophy of animal liberation––still a contentious matter today.

Hume is perhaps most famous for his correct assertion that the body also generates and limits our capacity for rational thought, and that reason is subject to the whims of emotion (passion). His observance that “Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them” has proved more valid than not, although our understanding of this relationship has come a long way in the intervening centuries (295). We now know that reason can’t exist without emotion (at least not in humans), but also that we have the capacity to override our emotions given sufficient motivation and favorable circumstances. It’s less like a master/slave relationship and more like two dancing partners with different skill sets and no clear leader.

If he favors the passions overmuch, Hume at least has good reasons for doing so (ironic, right?). For Hume, the passions provide the foundation not just for reason, but for morality as well. Morality is embodied––our moral judgments are rooted in sentiments of pleasure and pain that become abstracted and institutionalized via individual habit and social custom. This process is enabled by the same phenomenon that binds us to other humans and animals: sympathy:

No quality of human nature is more remarkable, both in itself and in its consequences, than that propensity we have to sympathize with others, and to receive by communication their inclinations and sentiments, however different from, or even contrary to our own. (225)

To avoid the sometimes irksome distinction between sympathy and empathy, let’s use a different term: fellow feeling. Fellow feeling, for Hume, describes how our internal emotions naturally imitate the emotions of those around us (this general phenomenon has been validated by the discovery of mirror neuron systems).

Hume posits that our natural inclination is to satisfy our self-interest, but under ideal conditions we learn to situate our self-interest within the context of the greater good:

After men have found by experience, that their selfishness and confin’d generosity, acting at their liberty, totally incapacitate them for society; and at the same time have observ’d, that society is necessary to the satisfaction of those very passions, they are naturally induc’d to lay themselves under the restraint of such rules, as may render their commerce more safe and commodious. (354)

This is the seed of what evolutionary theorists call reciprocal altruism. Further, the influence of fellow feeling reaches all the way into our conceptualizations of social justice:

Every thing, which gives uneasiness in human actions, upon the general survey, is call’d Vice, and whatever produces satisfaction, in the same manner, is denominated Virtue; this is the reason why the sense of moral good and evil follows upon justice and injustice. And tho’ this sense, in the present case, be deriv’d only from contemplating the actions of others, yet we fail not to extend it ever to our own actions. The generals rule reaches beyond those instances, from which it arose; while at the same time we naturally sympathize with others in the sentiments they entertain of us. Thus self-interest is the original motive to the establishment of justice: but a sympathy with public interest is the source of the moral approbation, which attends that virtue. (355, emphasis his)

The significance of Hume’s tireless efforts to bring human sentiment to the forefront of philosophical discourse cannot be overstated. It is because of such thinkers that, centuries later, we have a rich and mutable scientific and philosophical discourse about how we should conduct ourselves based on our experience as embodied beings. John Dewey, my favorite philosopher and a great champion of embodied rationality, owes much to texts like this one.

All great philosophical texts leave us with at least one great unanswered question. The question I find most relevant from this text is how societies can help individuals strike a balance between our natural self-interest and the common good, taking advantage of any many positive-sum situations as possible. As Hume explains, we have trouble foregoing immediate pleasures in favor of the general interest of society, which feels far more remote:

As it is impossible to change or correct any thing material in our nature, the utmost we can do is to change our circumstances and situation, and render the observance of the laws of justice our nearest interest, and their violation our most remote…Here then is the origin of civil government and society. Men are not able radically to cure, either in themselves or others, that narrowness of soul, which makes them prefer the present to the remote. They cannot change their natures. All they can do is to change their situation, and render the observance of justice the immediate interest of some particular persons, and its violation their more remote. (382-3)

While I don’t think it’s impossible to change human nature in an absolute sense, Hume is correct that actual progress almost always comes from changing the conditions in which human commerce and decisions occur. The general goal is clear: the more we provide people with the time and tools to explore a broad horizon of possible actions and futures, the better off we’ll all be.

How to do this?

I must plead the privilege of a sceptic, and confess, that this difficulty is too hard for my understanding. I pretend not, however, to pronounce it absolutely insuperable. Others, perhaps, or myself, upon more mature reflexions, may discover some hypothesis, that will reconcile those contradictions. (452)

Rating: 8/10