C. I. Lewis

A Pragmatic Conception of the A Priori

Example of the a priori par excellence: laws of logic: e.g., the law of (non)contradiction which demands that something (sufficiently qualified and defined) cannot be both true AND false at the same time (p & ~p = F). • This principle still perfectly – or consistently – applies to something that is true in one respect and false in another, logically represented as p & q, where q looks a lot like not p exactly because it has NOT been sufficiently qualified and defined. Simply stated, what is being referred to as ~p in fact does not negate p (hence, the schematization should be p & q instead of p & ~p). • “The laws of logic are purely formal; they forbid nothing but what concerns the use of terms and the corresponding modes of classification and analysis” (p. 365). • However, if we are to “discover what contradicts what we must always consult the character of experience” (p. 365).

A Survey of Symbolic Logic.

Modern interest in modal logic began with this seminal work by the American C.I. Lewis. As well as developing a theory of strict implication based on criticism of Russell and Whitebreads concept of implication, it contains historical information on the history and application of algebra to developments in symbolic logic.