Hume, the most misunderstood philosopher

We grant that the Treatise may not be a entirely consistent work and that its precise aim may still be quite unclear.  But this does not erase the fact that Hume has suffered historically from being appropriated, perverted and misrepresented by subsequent generations.   Hume has had only few serious readers or quasi-genuine readers such as Kant, T. H. Green, Brentano, Meinong, Husserl and Whitehead.

The problem with Hume is that he does not seem to be able to make up his mind if he is engaging in a radical philosophy in the style of Descartes or in a rational and experimental psychology.

The philosophy of Hume is radically incompatible with subsequent naturalism, so-called empiricism or logical positivism.

The philosophy of Hume is not compatible with the kind of relativism or skepticism exemplified by Sextus Empiricus (whom Hume most certainly read).  On the contrary Hume values highly evidence and rigorous proof.  Consider this beautifully embarrassing passage from part II of section II (Book I):

But here we may observe, that nothing can be more absurd, than this custom of calling a difficulty what pretends to be a demonstration, and endeavouring by that means to elude its force and evidence. It is not in demonstrations as in probabilities, that difficulties can take place, and one argument counter-ballance another, and diminish its authority. A demonstration, if just, admits of no opposite difficulty; and if not just, it is a mere sophism, and consequently can never be a difficulty. It is either irresistible, or has no manner of force. To talk therefore of objections and replies, and ballancing of arguments in such a question as this, is to confess, either that human reason is nothing but a play of words, or that the person himself, who talks so, has not a Capacity equal to such subjects. Demonstrations may be difficult to be comprehended, because of abstractedness of the subject; but can never have such difficulties as will weaken their authority, when once they are comprehended.

Goodbye Sextus !

Hume was forced to admit that there is a process of abstraction applied even to the most elementary, simple, indecomposable impressions like  colored points. Hume uses in various passages the expression under a certain light.

Suppose that in the extended object, or composition of coloured points, from which we first received the idea of extension, the points were of a purple colour; it follows, that in every repetition of that idea we would not only place the points in the same order with respect to each other, but also bestow on them that precise colour, with which alone we are acquainted. But afterwards having experience of the other colours of violet, green, red, white, black, and of all the different compositions of these, and finding a resemblance in the disposition of coloured points, of which they are composed, we omit the peculiarities of colour, as far as possible, and found an abstract idea merely on that disposition of points, or manner of appearance, in which they agree. Nay even when the resemblance is carryed beyond the objects of one sense, and the impressions of touch are found to be Similar to those of sight in the disposition of their parts; this does not hinder the abstract idea from representing both, upon account of their resemblance. All abstract ideas are really nothing but particular ones, considered in a certain light; but being annexed to general terms, they are able to represent a vast variety, and to comprehend objects, which, as they are alike in some particulars, are in others vastly wide of each other.  (part III, section II)

Finally, Hume has given us one of the most beautiful expressions of subjective idealism in the famous passage (end of section II):

We may observe, that it is universally allowed by philosophers, and is besides pretty obvious of itself, that nothing is ever really present with the mind but its perceptions or impressions and ideas, and that external objects become known to us only by those perceptions they occasion. To hate, to love, to think, to feel, to see; all this is nothing but to perceive. Now since nothing is ever present to the mind but perceptions, and since all ideas are derived from something antecedently present to the mind; it follows, that it is impossible for us so much as to conceive or form an idea of any thing specifically different from ideas and impressions. Let us fix our attention out of ourselves as much as possible: Let us chase our imagination to the heavens, or to the utmost limits of the universe; we never really advance a step beyond ourselves, nor can conceive any kind of existence, but those perceptions, which have appeared in that narrow compass. This is the universe of the imagination, nor have we any idea but what is there produced.