Synonyms for Theorize:

n.

assess, think out, evaluate, take something into consideration, take a long hard look at someone/something. thoughts, belief. theorize (noun)
theorise, conjecture, hypothesize, suppose, hypothesise, speculate, hypothecate.

v.

hypothesize (verb)
conjecture, speculate, guess, think, suppose.
imagine (verb)
consider, observe, conceive, contemplate, fantasize, envision, create, imagine, suppose, opine, think, invent, reflect, plan, design, ideate, perceive, brainstorm.
suppose (verb)
speculate, conjecture, philosophize, prophesy, hypothesize, presume, guess.

Other synonyms:

Other relevant words:
thoughts, assess, hypothecate, theorise, evaluate, hypothesise, belief.