The Collaborative International Dictionary of English v.0.48:

Theorization \The`o*ri*za"tion\, n.
   The act or product of theorizing; the formation of a theory
   or theories; speculation.
   [1913 Webster]

WordNet (r) 3.0 (2006):

theorization
    n 1: the production or use of theories [syn: theorization,
         theorisation]