On the Mysteries (De Mysteriis)

...[intel]lect, and is formed by intelligence, which they call the acquired intellect intellectus adeptus: in medieval and Renaissance philosophy, this is the human mind once it has been fully "perfected" or filled with divine truths. For the first knowledge consists in the active intellect intellectus agens: the part of the mind that actively processes information and "lights up" our understanding. Since knowledge occurs through conformity original: adaequationem; the philosophical idea that the mind must "match" or become like the object it is trying to understand, it follows that we reach even the smallest eternal and immovable things through an eternal, immovable, and simple notion.

The knowledge by which we know separate substances substantiae separatae: spiritual beings that exist independently of physical bodies, such as angels or the higher gods is of a different kind than that by which we know other things. Knowledge of divine things has always been in the soul through a simple intuition original: simplicem intuitum; a direct "seeing" or flash of insight rather than logical step-by-step thinking or contact.

Some think they will reach these separate beings through a certain method of opposition—namely, that [material things] are material, movable, localized, and subject to change; therefore, separate beings are immovable, etc. In this way, one certainly learns what they are not, but what they truly are is known by the conformity of our knowledge to that which is naturally present in the soul through the intellect. This is acquired in the rational power through a certain study, not so much of comparison and conjecture, but through the duty of separation and purification original: separationis, & purificationis officio; the practice of mentally "cleaning" the mind of worldly distractions to perceive spiritual reality. There was also a method of disjunction: for example, the gods and divine things are either temporal or eternal. Since they are not temporal, they must be eternal, and so forth. Yet even this method, due to its own shifting nature original: mobilitate; refers to the way logical arguments move from one step to the next, which is unlike the unchanging nature of the gods, does not suit those things which are immovable.

On the properties of each of the higher beings.

If any composition, on the contrary, exists within separate and separable substances, it is not...