Summary: A Treatise of Human Nature (page 10)

Here is a second formulation of the mechanism of the imagination that leads us to believe in the fiction of an external world continuous and independent of our perceptions:

Our memory presents us with a vast number of instances of perceptions perfectly resembling each other, that return at different distances of time, and after considerable interruptions. This resemblance gives us a propension to consider these interrupted perceptions as the same; and also a propension to connect them by a continu'd existence, in order to justify this identity, and avoid the contradiction, in which the interrupted apperance of these perceptions seems necessarily to involve us.

Here then we have a propensity to feign the continu'd existence of all sensible objects; and as this propensity arises from some lively impressions of the memory, it bestows a vivacity on that fiction; or in other words, makes us believe the continu'd existence of body ¹.

Hume insists: this is a fiction: This propension to bestow an identity on our resembling perception, produces the fiction of a continu'd existence; since that fiction, as well as the identity, is really false, as is acknowledg'd by all philosophers, and has no other effect than to remedy the interruption of our perceptions ².

The fiction of identity can never arise from reason, but must arise from the imagination ³.

Hume remarks that there is an intimate connexion betwixt those two principles, of a continu'd and of a distinct or independent existence, and that we no sooner establish the one than the other follows, as a necessary consequence. 'Tis the opinion of a continu'd existence, which first takes place, and without much study or reflection draws the other along with it ⁴.

Hume now examines the sleights of hand that philosophers have devised to escape this difficulty and attempt to ground rationally the existence of a continuous and independent external world.

Since it is obvious that perceptions have a discontinuous existence, philosophers have distinguished between perceptions and objects, of which the former are suppos'd to be interrupted, and perishing, and different at every different return; the latter to be uninterrupted and to preserve a continu'd existence and identity ⁵.

Yet this does not satisfy Hume: this system is only a palliative remedy, and [...] it contains all the difficulties of the vulgar system, with some others, that are peculiar to itself ⁶.

In effect, this amounts to supposing that on one side stands the object, and on the other our perception of it, and that the former is the cause of the latter.

Here Hume recalls what Berkeley had already made plain: No beings are ever present to the mind but perceptions ⁷.

From this it follows that we may observe a conjunction or a relation of cause and effect betwixt different perceptions, but can never observe it betwixt perceptions and objects ⁸.

Hume concludes: 'Tis impossible, therefore, that from the existence or any of the qualities of the former, we can ever form any conclusion concerning the existence of the latter, or ever satisfy our reason in this particular ⁹.

We can see that, for all his harsh words against the sceptics at the outset, Hume's conclusion is eminently sceptical.

We can never know whether there exists a real world that is external, continuous, and independent of the human mind. The object is forever out of reach; we have only perceptions of it, and must make do with a few coherences and regularities in the shifting flow of perceptions—a chaos that the imagination strives, however hard it tries, to bring into order.

Hume ends on an ironic note: The notion of an independent and continu'd existence [...] has taken such deep root in the imagination, that 'tis impossible ever to eradicate it, nor will any strain'd metaphysical conviction of the dependence of our perceptions be sufficient for that purpose ¹⁰.

So if reflection leads us to sceptical doubt, carelesness and in-attention alone can afford us any remedy. For this reason I rely entirely upon them; and take it for granted, whatever may be the reader's opinion at this present moment, that an hour hence he will be perswaded there is both an external and internal world ¹¹.

For Hume, the only indubitable fact is this: we have perceptions that are discontinuous and dependent on us. That is all that can be said. We cannot infer from them the existence of objects, nor of a continuous external world independent of us.

Yet philosophers have forged a concept that might seem to resolve miraculously the problems we have just encountered: that of substance.

Substance is what would underlie these discontinuous perceptions, remaining one and self-identical. Hume therefore devotes an entire section to this notion, aptly titled "Of the antient philosophy":

I am perswaded, there might be several useful discoveries made from a criticism of the fictions of the antient philosophy, concerning substances, and substantial forms, and accidents, and occult qualities; which, however unreasonable and capricious, have a very intimate connexion with the principles of human nature ¹².

Substance: an ancient, Aristotelian notion, enshrined by medieval Scholasticism, which Hume attacks, following Berkeley.

The notion of substance seems essential to the constitution of that of object.

When I consider an object—take this piece of wax—I perceive only a set of sensible qualities: a certain texture to the touch, a certain colour, a smell, and so on.

How do I gather these distinct sensible qualities into a single object?

Here is a new leap that needs to be justified—and we can guess where Hume will come down.

He sums up this new fundamental problem as follows:

'Tis confest by the most judicious philosophers , that our ideas of bodies are nothing but collections form'd by the mind of the ideas of the several distinct sensible qualities, of which, objects are compos'd, and which we find to have a constant union with each other.

But however these qualities may in themselves be entirely distinct, 'tis certain we commonly regard the compound, which they form, as ONE thing, and as continuing the SAME under very considerable alterations.

The acknowledg'd composition is evidently contrary to this suppos'd simplicity, and the variation to the identity.

It may, therefore, be worth while to consider the causes, which make us almost universally fall into such evident contraditions, as well as the means by which we endeavour to conceal them ¹³.

Let us see how, in just a few pages, Hume manages to dissolve and dispel the very notion of object.

¹ 1.4.2, p.138
² P.139
³ Ibid.
⁴ Ibid.
⁵ p.140
⁶ Ibid.
⁷ P.140-141
⁸ P.141
⁹ Ibid.
¹⁰ P.142
¹¹ P.144
¹² 1.4.3, p.145
¹³ Ibid.