Sensations

   1) The Existence of Our Sensations Is Indisputable

   Nothing is more indisputable than the existence of our sensations. Thus, in order to prove that they are the principle of all our knowledge, it suffices to show that they can be. . . . Why suppose that we have purely intellectual notions at the outset if all we need do in order to form them is to reflect upon our sensations? (D'Alembert, 1963, p. 7)

   2) The Source of Belief in Sensations

   [S]upposing we have got the conception of hardness, how come we by the belief of it? Is it self-evident, from comparing the ideas, that such a sensation could not be felt unless such a quality of bodies existed? No. Can it be proved by probability or certain arguments? No. Have we got this belief then by tradition, by education, or by experience? No. . . . Shall we then throw off this belief, as having no foundation in reason? Alas! it is not in our power; it triumphs over reason, and laughs at all the arguments of a philosopher. Even the author of the "Treatise of Human Nature," though he saw no reason for this belief . . . could hardly conquer it in his speculative and solitary moments; at other times he fairly yielded to it, and confesses that he found himself under a necessity to do so. (Reid, 1970, p. 157)