September 23. 1830
Logic
There are two kinds of logic: 1. Syllogistic. 2. Criterional. How any one can by any spinning make out more than ten or a dozen pages about the first, is inconceivable to me; all those absurd forms of syllogisms are one half pure sophisms, and the other half mere forms of rhetoric.
All syllogistic logic is—1. Seclusion; 2. Inclusion; 3. Conclusion; which answer to the understanding, the experience, and the reason. The first says, this ought to be; the second adds, this is; and the last pronounces, this must be so. The criterional logic, or logic of premisses, is, of course, much the most important; and it has never yet been treated.
The object of rhetoric is persuasion,—of logic, conviction,—of grammar, significancy. A fourth term is wanting, the rhematic, or logic of sentences.