Abstract
At the very end of the Essay Concerning Human Understanding, Locke sets forth a division of the sciences. He sees science as having three branches. The first he calls "natural philosophy" or "physica" (IV, 21, 2, p. 442). Its concern is the "nature of things, as they are in themselves, their relations, and their manner of operation" (IV, 21, 1, p. 442). The second he calls "ethics" or "practica" (IV, 21, 3, p. 442). Its object of study is what "man himself ought to do, as a rational and voluntary agent, for the attainment of any end, especially happiness" (IV, 21, 1, p. 442). The third science he calls "the doctrine of signs" or "semeiotic?" (IV, 21, 4, p. 443). Its field of study is "the ways and means whereby the knowledge of both [natural philosophy] and [ethics] are attained and communicated" (IV, 21, 1, p. 442).
This division of the sciences, it seems, is based upon a difference in the objects of study with which each is concerned. Natural philosophy is concerned with things as they are in themselves, and ethics is concerned with human actions aimed at an end, particularly happiness. These areas of study seem to be rather clearly set forth.
However, the domain of the third science, semeiotic?, raises a perplexing question. Locke declares that its objects are the signs which "the mind makes use of for the understanding of things, or conveying its knowledge to others" (IV, 21, 4, p. 443). It would seem, then, that the science of semeiotic? would be concerned with words, since words are commonly considered to be signs.
To be sure, the science of semeiotic? is concerned with words. However, it is also concerned with ideas. It is concerned with ideas and words as the great instruments of knowledge (IV, 21, 4, p. 443). Ideas, though, are not commonly considered to be signs. Thus the question arises why Locke considers ideas to be such.
