To begin very near indeed to the beginning, let us take, first, the section of the 'Enquiry' which treats of the 'Origin of Ideas.' All the perceptions of the mind may, according to Hume, be divided into two classes, whereof the one consists of all those 'more lively perceptions,' termed by him indifferently Impressions or Sensations, which we experience when we 'hear, or see, or feel, or love, or hate, or desire, or will:' the other, of those 'less lively perceptions of which we are conscious when we reflect on any of the sensations above-mentioned,' and which are commonly denominated thoughts or ideas. 'All our ideas or more feeble perceptions,' he continues, 'are copies of our impressions or more lively ones,' the 'entire creative power of the mind amounting to no more than the faculty of compounding, transposing, augmenting, or diminishing the materials afforded by the senses and experience.' So confident is he of the literal accuracy of this statement, as to proceed to intimate that whenever we find in conversation or argument 'a philosophical term employed seemingly without any idea or meaning,' we have only to enquire from what impression its idea, if it have one, is derived, when, if no impression can be adduced, we may be sure that no idea is present either. The only phenomenon opposed to this rule, which he professes himself able to think of, is that of a person who, of a colour--as, for instance, blue--with which he is familiar, is able to conceive a shade somewhat different from any of the shades which he has actually seen; but this instance he disregards as too singular to affect the general maxim, to which, as he might have added, it is not really an exception, any more than would be the power of a person who had never seen a mountain higher than Snowdon or Mont Blanc to conceive one as high as Chimborazo or Mount Everest, for, equally in both cases, the ideas are copies of sensible impressions, although of complex, not simple, ones--of colour and graduation in the first case, of size and increase in the second. Still, there is at least one genuine exception, which it is the more remarkable that Hume should have overlooked, as it may be said to have stared him in the face from the very subject-matter he was considering. Our idea of idea itself, from what sensible impression is that derived? We have just been told that the difference between an idea and a sensation is that the first is a copy of the second, a feeble copy of a lively original. The idea therefore is not itself a sensation; the copy is not itself an original. Neither consequently can the idea or notion which the mind proceeds to form of any of its previous ideas be derived from or be a copy of a sensation: it cannot have entered the mind 'in the only manner by which,' according to Hume, 'an idea can have access to the mind, to wit, by actual feeling and sensation.'