Digital Companion to C. S. Peirce
1901-1902 [c.] | Definitions for Baldwin's Dictionary [R] | MS [R] 1147

Theory [—] An outline statement, presenting to contemplation a sort of ideal diagram, or construction, which is to serve to represent a series of facts, not as they first present themselves, but so as to render the relations between them comprehensible. Theory is used in opposition to fact, and also in opposition to practice.

1902 | Theory (in science) | DPP 2:693

The whole aim of science is to find out facts, and to work out a satisfactory theory of them. Still, a theory does not necessarily lose its utility by not being altogether true. It must be intelligible and diagrammatical, or it has no title to the name theory. The facts to which it refers are not necessarily facts of experience; they may be relations of pure mathematical forms. A theory is properly a result of systematic scientific consideration, not of mere casual suggestions; and thus the word bears a somewhat eulogistic implication in contrast to ‘view.’ Theory is opposed to fact; the latter meaning, in this connection, that which is forced upon us by perception; while theory is the part of science which is contributed by the intellect and confirmed by experiment. Theory is also opposed to practice; because a theory is a scientific product, and a pure, or theoretical, theory has regard to science alone, and is often in conflict with the practical theory, which ought preferably to be the guide of immediate action. But the latter is as truly a theory as the former, and ought equally (when practicable) to be a product of scientific examination.

1904 [c.] | New Elements (Kaina stoiceia) | EP 2:304-5

Of the two great tasks of humanity, Theory and Practice, the former sets out from a sign of a real object with which it is acquainted, passing from this, as its matter, to successive interpretants embodying more and more fully its form, wishing ultimately to reach a direct perception of the entelechy; while the latter, setting out from a sign signifying a character of which it has an idea, passes from this, as its form, to successive interpretants realizing more and more precisely its matter, hoping ultimately to be able to make a direct effort, producing the entelechy. But of these two movements, logic very properly prefers to take that of Theory as the primary one.