"But," it may be said, "though we cannot directly knowconsciousness to be finite in duration, because neither of its limits canbe actually reached, yet we can very well conceive it to be so." No: not even this is true. We cannot conceive the terminations of that consciousnesswhich alone we really know -- our own -- any more than we can perceive itsterminations. For in truth the two acts are here one. In either case suchterminations must be, as above said, not presented in thought, but represented;and they must be represented as in the act of occurring. Now to representthe termination of consciousness as occurring in ourselves, is to think ofourselves as contemplating the cessation of the last state of consciousness;and this implies a supposed continuance of consciousness after its last state,which is absurd.

Hence, while we are unable to believe or to conceive that the durationof consciousness is infinite, we are equally unable either to know it asfinite, or to conceive it as finite: we can only infer from indirect evidencethat it is finite. §20. Nor do we meet with any greater success when, instead of theextent of consciousness, we consider its substance. The question -- Whatis this that thinks? admits of no better solution than the question to whichwe have just found none but inconceivable answers.

The existence of each individual as known to himself, has always beenheld the most incontrovertible of truths. To say -- "I am as sure ofit as I am sure that I exist," is, in common speech, the most emphaticexpression of certainty. And this fact of personal existence, testified toby the universal consciousness of men, has been made the basis of more philosophiesthan one.

Belief in the reality of self cannot, indeed, be escaped while normalconsciousness continues. What shall we say of these successive impressionsand ideas which constitute consciousness? Are they affections of somethingcalled mind, which, as being the subject of them, is the real ego? If wesay this we imply that the ego is an entity. Shall we assert that these impressionsand ideas are not the mere superficial changes wrought on some thinking substance,but are themselves the very body of this substance -- are severally the modifiedforms which it from moment to moment assumes? This hypothesis, equally withthe foregoing, implies that the conscious self exists as a permanent continuousbeing; since modifications necessarily involve something modified. Shallwe then betake ourselves to the sceptic's position, and argue that our impressionsand ideas themselves are to us the only existences, and that the personalitysaid to underlie them is a fiction? We do not even thus escape; since thisproposition, verbally intelligible but really unthinkable, itself makes theassumption which it professes to repudiate. For how can consciousness bewholly resolved into impressions and ideas, when an impression of necessityimples something impressed? Or again, how can the sceptic who has decomposedhis consciousness into impressions and ideas, explain the fact that he considersthem as his impressions and ideas? Or once more, if, as he must, he admitsthat he has an impression of his personal existence, what warrant can heshow for rejecting this impression as unreal while he accepts all his otherimpressions as real?