Epistemology
"Whatever is in our intellect must have previously been in the senses." —St. Thomas Aquinas, the peripatetic axiom.Thomas adhered to the correspondence theory of truth, which says that something is true "when it conforms to the external reality." Therefore, any being that exists can be said to be true insofar that it participates in the world.
Aristotle's De anima (On the Soul) divides the mind into three parts: sensation, imagination and intellection. When one perceives an object, his mind composites a sense-image. When he remembers the object he previously sensed, he is imagining its form (the image of the imagination is often translated as "phantasm"). When he extracts information from this phantasm, he is using his intellect. Consequently, all human knowledge concerning universals (such as species and properties) are derived from the phantasm ("the received is in the receiver according to the mode of the receiver"), which itself is a recollection of an experience. Concerning the question of "Whether the intellect can actually understand through the intelligible species of which it is possessed, without turning to the phantasms?" in the Summa Theologica, Thomas quotes Aristotle in the sed contra: "the soul understands nothing without a phantasm." Hence the peripatetic axiom. (Another theorem to be drawn from this is that error is a result of drawing false conclusions based on our sensations.)
Thomas's epistemological theory would later be classified as empiricism, for holding that sensations are a necessary step in acquiring knowledge, and that deductions cannot be made from pure reason.
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