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Webster 1913 Edition

Adj.

Making; having power to make.

[Obs.]

“You are . . . factive, not destructive.”

Bacon.

Adj.

Making; having power to make. [Not used.]

factive ‎(not comparable)

(linguistics, of a verb) Licensing only those content clauses that represent claims assumed to be true.
You can't say that somebody "discovered" the Moon to be made of green cheese, because "discover" is a factive verb and the Moon isn't made of green cheese.
(epistemology, of a knowing agent) which does not know any falsities: which knows only truths.