The Commens Dictionary
Quote from ‘Telepathy’
… what is an index, or true symptom? It is something which, without any rational necessitation, is forced by blind fact to correspond to its object.
‘Index’ (pub. 05.05.13-10:26). 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-telepathy-0.