The Commens Dictionary
Quote from ‘Suggestions for a Course of Entretiens leading up through Philosophy to the Questions of Spiritualism, Ghosts, and finally to that of Religion’
The second kind of reasoning is Deduction. This is necessary reasoning. That is it makes the truth of the conclusion whensoever the premisses may be true, to be evident. The premisses, in so far as they determine the character of the conclusion, are merely hypothetical. The evidence consists in the fact that the state of things which they suppose is fully diagrammatized so that one can see that a modification which adds nothing to the supposed condition connects the premisses into the conclusion.
MS [R] 876:3-4
‘Deduction’ (pub. 19.10.15-19:35). Quote in M. Bergman & S. Paavola (Eds.), The Commens Dictionary: Peirce's Terms in His Own Words. New Edition. Retrieved from http://www.commens.org/dictionary/entry/quote-suggestions-course-entretiens-leading-through-philosophy-questions-0.