There is a dual operation to the intellect. Aquinas believed that several sensations grouped together would create a memory, and that many memories grouped together equal sense experience. Sense knowledge is only understandable by the action of the intellect. Sense memory allows the individual to reproduce in one's memory an image they had seen. Sense-consciousness gives an awareness of an object through various sense perceptions.
Instinct relates to a particular concrete connection such as an individual fleeing from fire.
Imagination takes materials supplied through sense memory and translates them into a particular image composed of characters derived from other images. The second type of knowledge, intellectual knowledge, is abstract and general. This knowledge is quite different from the concrete and particular of external and internal senses. The general ability to understand covers simple apprehension, judgment, and reasoning. Simple apprehension is when the mind accepts an object without affirming or denying it.