theorize

(verb) to believe especially on uncertain or tentative grounds. Synonyms: speculate, theorise, conjecture, hypothesize, hypothesise, hypothecate, suppose. Example: "Scientists supposed that large dinosaurs lived in swamps."

(verb) construct a theory about. Example: "Galileo theorized the motion of the stars."

(verb) form or construct theories. Example: "He thinks and theorizes all day."