Phantasia

Phantasia is the power of the mind to form and retain images (phantasmata) — what we call imagination. For Aristotle it stands between perception and thought: it preserves and recombines the impressions of the senses, supplies the images without which the mind cannot think, and underlies memory and dreams.

The Stoics gave the word a central role in their theory of knowledge: a phantasia is the 'impression' stamped on the soul by what we perceive, and wisdom lies in assenting only to those impressions that are clear and true, withholding judgment from the rest. So imagination became the gatekeeper between the world and the soul's beliefs.