The Commens Dictionary

Quote from ‘Minute Logic: Chapter I. Intended Characters of this Treatise’

That our thoughts are signs is an old and familiar doctrine. I show that it is only in so far as thoughts are signs, and particularly […] symbols, that they become subjects of logic; and further that the rules of logic are applicable to all symbols. Accordingly by regarding logic as a science of signs or formal semeiotic, and in the main as a science of symbols, or formal symbolic, we accurately cover its subject matter, and at the same time insure ourselves against all risk of being led astray into psychology. The word formal, in this connection, signifies that only the general conditions to which signs ought to conform are to be considered.

But those conditions may be distinguished into three kinds, leading to a corresponding distinction between three departments of logic, in its wider sense; or Formal Semeiotic. Namely the conditions are either, first, such as must be fulfilled in order that an object may be a sign at all; second, such as must be fulfilled in order that the sign may refer to the object to which it aims to refer, that is, may be true; and third, such as must be fulfilled in order that the sign may determine the interpretant it aims to determine, that is, may be pertinent. [—] The study of the second series of conditions is Logic in its narrow sense, or, as we may call it, Critical Logic.