Logos

From Conservapedia

"Logos" is the Greek term used by St. John to describe the second person of the Holy Trinity, the Word of God. In Greek "logos" means word, reason or speech.

In literature, logos refers to an appeal to logic, as opposed to an appeal to emotion (pathos) or an appeal to authority (ethos).

Also see

Heraclitus (circa 535–475 BC)