The Commens Dictionary
Quote from ‘Reason's Rules’
No matter how completely free the Reader may be of the influence of logical systems and traditions, he nevertheless does hold certain logical tenets. There are certain general forms of reasoning which he approves as calculated to lead to the truth. There are certain others which he condemns as dangerous. This doctrine is his logica utens; and he actually applies it in every case in which he can properly be said to reason.
MS [R] 596:17-18
‘Logica Utens’ (pub. 15.08.17-19:24). 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-reasons-rules-19.