177. All ideological labors commence then by establishing the fact of consciousness of our ideas; and it cannot be otherwise with respect to their certainty. Man, although he overthrow and destroy every thing, still encounters himself, the one who overthrows and destroys every thing. When he has gone so far as to doubt the existence of God, the world, his fellow-beings, his own body, he still, in the midst of this immense solitude, encounters himself. The effort to conceal himself from his own eyes serves only to render him more visible: he is a spirit to be killed by no blow, and rays of light flow from every wound inflicted on him. If he doubts that he feels, he at least feels that he doubts; if he doubts of this doubt, he feels that he doubts of doubt itself; thus, in doubting of direct acts, he enters into an interminable series of reflex acts, necessarily linked one with the other, and unrolled to the internal view like folds of a scarf which has no end.(18) CHAPTER XIX. VALUE OF THE PRINCIPLE, I THINK: ITS--ANALYSIS. 178. We have already seen that Descartes' principle, considered as an enthymema, cannot aspire to be fundamental. In every argument there are premises and a consequence; and to be conclusive, the premises must be true, and the consequence legitimate. To say that an argument may be a fundamental principle, is a manifest contradiction. But if we take Descartes' principle in the sense above explained, that is, not as an argument but as the declaration of a fact, the contradiction ceases, and it is a question, worthy to be examined, whether it merits the title of fundamental principle or not, and in what sense. We have already somewhat illustrated this matter, but not yet sufficiently cleared it up; we have made some preliminary remarks in order to show the state of the question, but have not yet completely solved it. 179. The proposition, _I think_, as we have remarked, expresses something more than merely thought, strictly so called: it embraces acts of the will, sentiments, sensations, acts, and expressions of all kinds which are realized within us; it includes all phenomena immediately present to our mind, and attested by consciousness. Nothing that distinguishes between various acts and impressions can be a fundamental principle: such a distinction supposes analysis, and analysis requires reflection. We do not reflect without rules and objects already known; consequently, to admit classifications in the first principle, is to divest it of its character and to contradict ourselves. 180. We must not confound what is expressed by the proposition _I think_ with the proposition itself. The thing itself and the form are here very different: the nature of the form may make us conceive ambiguous ideas of the thing itself: the thing itself is a most simple fact; the form is a logical combination, and includes very heterogeneous elements. This demands explanation.