a. [ L. illativus: cf. F. illatif. ] Relating to, dependent on, or denoting, illation; inferential; conclusive; as, an illative consequence or proposition; an illative word, as then, therefore, etc. [ 1913 Webster ]

Illative conversion (Logic), a converse or reverse statement of a proposition which in that form must be true because the original proposition is true. --
Illative sense (Metaph.), the faculty of the mind by which it apprehends the conditions and determines upon the correctness of inferences. [ 1913 Webster ]

n. An illative particle, as for, because. [ 1913 Webster ]

adv. By inference; as an illative; in an illative manner. [ 1913 Webster ]