The self and mitigated skepticism

Descartes had made the self the bedrock of all knowledge: the res cogitans (thinking thing), a simple, unified substance whose existence is the one thing I cannot doubt. Locke had softened it into a self constituted by continuity of consciousness and memory. Hume now aims his Copy Principle at both. If we really have an idea of a self — a simple thing, identical through the whole of life — then, by his rule, from what impression is it derived?

The demand is fatal. A single, unchanging self would have to spring from a single, unchanging impression lasting a lifetime. But no such impression exists: our impressions — heat and cold, love and hatred, pain and pleasure — constantly succeed one another and never all coexist. There is no steady, invariable impression of a self. So, by the Copy Principle, there is no idea of such a self (Treatise I.iv.6).

Then Hume runs the famous introspective experiment. He enters “most intimately” into what he calls himself, and reports what he finds:

“I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception.” (Treatise I.iv.6)

He never catches a bare self; he catches only perceptions. And when the perceptions are removed — in deep sleep — he is, for that time, insensible of himself, and “may truly be said not to exist.”

From this comes Hume’s bundle theory: the mind 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.” There is no underlying thing that has the perceptions; there is only the perceptions themselves, streaming. The self is not a container — it is the contents.

But then why does personal identity feel so obvious? Hume says it is a fiction manufactured by the imagination. As perceptions succeed one another, we notice resemblance (today’s memories resemble yesterday’s experiences) and causation (each perception influences the next), and these associative relations make the mind glide smoothly along the series. We confuse this easy, uninterrupted transition of thought with the survival of one unchanging thing — and so invent a self to underwrite an identity that is really just relatedness among ever-changing parts.

Step back and survey the wreckage. Hume’s empiricism has undermined our rational warrant for induction, for causal power, for the existence of the external world (an unperceived object is, again, an idea with no impression to ground it), and now for the self. Reason, followed honestly, seems to end in a radical skepticism that would make ordinary life impossible. Has Hume argued himself into paralysis?

No — because of a second force stronger than argument: nature. Reason may find no ground for these beliefs, but we are not free to give them up. “Nature, by an absolute and uncontroulable necessity, has determin’d us to judge as well as to breathe and feel.” The moment Hume leaves his study, plays a game of backgammon, dines and converses with friends, the skeptical doubts “vanish, and even the philosopher himself, after three or four hours’ amusement, would return to these speculations” only to find them cold and strained.

This yields Hume’s considered stance: mitigated skepticism (academical, as opposed to the excessive Pyrrhonian kind). Total, life-denying doubt is psychologically impossible and useless. What survives is a chastened doubt with two lasting effects: it breeds modesty and caution in all our reasonings, and it confines legitimate inquiry to subjects suited to our faculties — common life and the experimental sciences — while abandoning airy metaphysics beyond all experience.

Hume ends the Enquiry with the sharpest expression of this in all of philosophy. Take any volume of “divinity or school metaphysics,” he says, and ask whether it contains abstract reasoning about quantity or number (relations of ideas), or experimental reasoning about fact and existence (matters of fact). If it contains neither —

“Commit it then to the flames: for it can contain nothing but sophistry and illusion.” (Enquiry XII)

This is Hume’s Fork turned into a torch: whatever cannot be either a relation of ideas or a matter of fact has no genuine content and belongs in the fire.