  The most influential theory of thought in the thirteenth century goes back to Aristotle and has its foremost medieval defender in Thomas Aquinas. It rests on viewing mental representations or intelligible species, as Aquinas calls them, as sameness of form. The explanation for why thoughts are about something, exhibit intentionality, or represent is that the form of the object thought about is in the mind of the thinker. According to a popular metaphor, thinking something, on this view, is being the object thought about in the sense that the intellect becomes the object or takes on its form.