The Commens Dictionary
Quote from ‘Logical Tracts. No. 2. On Existential Graphs, Euler's Diagrams, and Logical Algebra’
The purpose of reasoning is to proceed from the recognition of the truth we already know to the knowledge of novel truth. This we may do by instinct or by a habit of which we are hardly conscious. But the operation is not worthy to be called reasoning unless it be deliberate, critical, self-controlled. In such genuine reasoning we are always conscious of proceeding according to a general rule which we approve. It may not be precisely formulated, but still we do think that all reasoning of that perhaps rather vaguely characterized kind will be safe. This is a doctrine of logic. We never can really reason without entertaining a logical theory. That is called our logica utens.
‘Logica Utens’ (pub. 01.02.13-19:20). 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-logical-tracts-no-2-existential-graphs-eulers-diagrams-and-logical-algebra.