verb (v)

• to believe especially on uncertain or tentative grounds(verb.cognition)

  Synonym:
  conjecture, hypothecate, hypothesise, hypothesize, speculate, suppose, theorise
  

  source: wordnet30
• construct a theory about(verb.cognition)

  Example:
  Galileo theorized the motion of the stars.
  

  source: wordnet30
• form or construct theories(verb.cognition)

  Example:
  He thinks and theorizes all day.
  

  source: wordnet30
• To form a theory or theories; to form opinions solely by theory; to speculate.(verb)

  source: webster1913