Book 3.3 is about the imagination. Many philosophers believe that thinking is perceiving. [At least, they use metaphors to describe thinking in terms of perceiving.] But this is not entirely the case because that would mean that everything that we see was true, and we are sometimes deceived by our senses. The sun, for example, looks small but is actually many times larger than the earth. But seeing things as they really are is always true, but it is possible to think falsely. Thought belongs to no creature which doesn’t have the power to reason.
Imagination is different from both perception and thought. It always implies perception, and is itself implied by judgment. It’s not in our power to form opinions about whatever we want because our opinions must be either true or false. When we form opinions we are immediately affected by them.
Imagination is a form of judgment, but it is not always right. Is it opinion?
“[O]pinion implies belief (for one cannot hold opinions in which one does not believe)” (428a20). Lower creatures don’t believe, but many have imagination. “Again, every opinion [doxa] is accompanied by belief [pistis], belief by conviction, and conviction by rational discourse [logos]” (428a20). Some creatures have imagination, but no reasoning power, no logos.
“Since sight is the chief sense, the name phantasia (imagination) is derived from phaos (light), because without light it is impossible to see” (429a).