first truth

first truth (plural first truths)

1. A statement that is not proved but rather supposed or held as obvious, forming together with other such statements the basis of a system of statements obtained from them by inference; an axiom.
   • 1836, John Abercrombie, Jacob Abbott, The Philosophy of the Moral Feelings‎:

     These are the principles also treated of, in a former work, under the name of First Truths. They are not, like our knowledge of the other kind, the result of any process either of investigation or of reasoning; and, for the possession of them, no man either depends upon his observation, or has recourse to that of other men.

• first principle