Note that these simple data or elements are not original, psychologically or historically; they are _logical_ primitives--that is, irreducible for purposes of inference. They are simply the most unambiguous and best defined objects of perception which can be secured to serve as _signs_. They are experimentally determined, with great art, precisely because the naturally given, the customary, objects in perception have been ambiguous or confused terms in inference. Hence they are replaced, through experimental means involving the use of wide scientific knowledge deductively employed, by simpler sense objects. Stated in current phraseology, "sensations" (i.e., qualities present to sense) are not the elements out of which perceptions are composed, constituted, or constructed; they are the finest, most carefully discriminated objects of perception. We do not first perceive a single, thoroughly defined shade, a tint and hue of red; its perception is the last refinement of observation. Such things are the limits of perception, but they are final, not initial, limits. They are what is perceived to be given under the most favorable possible conditions; conditions, moreover, which do not present themselves accidentally, but which have to be intentionally and experimentally established, and detection of which exacts the use of a vast body of scientific propositions. I hope it is now evident what was meant by saying that current logic presents us not with a confusion of psychology with logic, but with a wholesale mistaking of logical determinations for facts of psychology. The confusion was begun by Locke--or rather made completely current through the enormous influence exercised by Locke--and some reference to Locke may be of aid in clearing up the point. Locke's conception of knowledge was logical, not psychological. He meant by knowledge thoroughly justified beliefs or propositions, "certainty," and carefully distinguished it from what passed current as knowledge at a given time. The latter he called "assent," opinion, belief, or judgment. Moreover, his interest in the latter was logical. He was after an art of controlling the proper degree of assent to be given in matters of probability. In short, his sole aim was to determine certainty where certainty is possible and to determine the due degree of probability in the much vaster range of cases where only probability is attainable. A natural history of the growth of "knowledge" in the sense of what happens to pass for knowledge was the last of his interests. But he was completely under the domination of the ruling idea of his time; namely, that _Nature_ is the norm of truth. Now the earliest period of human life presents the "work of nature" in its pure and unadulterated form. The normal is the original, and the original is the normative. Nature is both beneficent and truthful in its work; it retains all the properties of the Supreme Being whose vice-regent it is. To get the logical ultimates we have