The Collaborative International Dictionary of English v.0.48:

Ratiocinative \Ra`ti*oc"i*na*tive\
   (r[a^]sh`[i^]*[o^]s"[i^]*n[asl]*t[i^]v), a. [L.
   ratiocinativus.]
   Characterized by, or addicted to, ratiocination; consisting
   in the comparison of propositions or facts, and the deduction
   of inferences from the comparison; argumentative; as, a
   ratiocinative process.
   [1913 Webster]

         The ratiocinative meditativeness of his character.
                                                  --Coleridge.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ratiocinative
    adj 1: based on exact thinking; "one's ratiocinative powers"