reasoner

from WordNet (r) 3.0 (2006)

reasoner
    n 1: someone who reasons logically [syn: {reasoner},
         {ratiocinator}]

from The Collaborative International Dictionary of English v.0.48

Reasoner \Rea"son*er\ (r[=e]"z'n*[~e]r), n.
   One who reasons or argues; as, a fair reasoner; a close
   reasoner; a logical reasoner.
   [1913 Webster]