Source : Webster's Revised Unabridged Dictionary (1913)

Illative \Il"la*tive\, 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.

   {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.

Illative \Il"la*tive\, n.
   An illative particle, as for, because.

Source : WordNet®

illative
     adj 1: relating to or having the nature of illation or inference;
            "the illative faculty of the mind" [syn: {inferential}]
     2: resembling or dependent on or arrived at by inference; "an
        illative conclusion"; "inferential reasoning" [syn: {inferential}]
     3: expressing or preceding an inference; "`therefore' is an
        illative word"