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Necessary Deduction

1903 | Graphs, Little Account [R] | MS [R] S27:1

*Necessary deduction* is that sort of inference in which the fact concluded is conceived to be involved in the facts premised. It is the reasoning of mathematical demonstration.

1903 | Syllabus: Nomenclature and Division of Triadic Relations, as far as they are determined | EP 2:298; CP 2.267

Necessary Deductions are those which have nothing to do with any ratio of frequency, but profess (or their interpretants profess for them) that from true premisses they must invariably produce true conclusions. A Necessary Deduction is a method of producing Dicent Symbols by the study of a diagram. It is either *Corollarial* or *Theorematic*. A Corollarial Deduction is one which represents the conditions of the conclusion in a diagram and finds from the observation of this diagram, as it is, the truth of the conclusion. A Theorematic Deduction is one which, having represented the conditions of the conclusion in a diagram, performs an ingenious experiment upon the diagram, and by the observation of the diagram, so modified, ascertains the truth of the conclusion.