Lamennais calls common sense the only criterion; nevertheless, we have only to glance at the others to be convinced that this new criterion is sterile, and could not produce them. 330. The testimony of consciousness, in the first place, cannot rest in any sense upon the authority of others. Formed as it is by a series of acts intimately present to our own mind, and, as without it, it is not possible for us even to conceive individual thought, it must evidently exist prior to the application of any criterion, since no criterion is possible to him who does not think. Under a scientific aspect nothing can be weaker than his pretended refutation of Descartes' principle. "When, trying to rise from his methodical doubt, Descartes establishes this proposition, _I think, therefore I am_, he passes an immense abyss, and lays in the clouds the corner-stone of the edifice he is about to raise; for, strictly speaking, we cannot say _I think_, we cannot say _I am_, we cannot say _therefore_, or affirm anything as a consequence."[34] [34] Ibid. Descartes' principle merited a more careful examination from whoever would invent a system. To oppose to it that we cannot say _therefore_, is to repeat the worn-out argument of the schools; and to affirm that we cannot say _I think_, is to contradict a fact of consciousness not denied even by skeptics. In place of this, we will explain at due length what is, or at least, what ought to be, the sense of Descartes' principle. If, according to Lamennais, we cannot say _I think_, still less can we say that others think; and as his system recognizes one only criterion, common consent, which absolutely needs the thought of others, it follows that Lamennais has laid his corner-stone higher in the clouds than he who founded philosophy upon a fact of consciousness. 331. A criterion, especially when it pretends to be the only one, ought to have these two conditions: to apply to all cases, and not to suppose another. Now the criterion of common consent is precisely that which is farthest from possessing these conditions: prior to it is the testimony of consciousness; prior also to it is the testimony of the senses, for we cannot know the consent of others if sight or hearing do not make us certain of it. 332. In many cases this criterion is impossible; in many others it is exceedingly difficult if not wholly impossible. To what point is common consent needed? If the word _common_ refers to the whole human race, how are the suffrages of all mankind to be recognized? If the consent need not be unanimous, to what point does the contradiction, or the simple non-assent of some, destroy the legitimacy of the criterion?