The word "matter" has a totally different meaning in ancient and medieval philosophy from that which it has in modern physics.
In modern physics, its usual significance lies in such phrases as "matter and energy." In fact, matter is a form of energy and can be transformed into it by the formula E = mc2, where c is the constant velocity of light. In quantum theory, especially in quantum electrodynamics (QED), matter obeys the laws of particle physics.
In Aristotelian philosophy, the word "matter" signifies potentiality. Pure potentiality, with no actuality, cannot exist. Existent matter, or what has been called signate matter, is formed of somewhat actualized potentiality. God is pure actuality because God is totally immaterial. The Greek word for form without matter, or pure actuality, is energeia, from which is derived the English word "energy."
In everyday speech, the word "matter" is usually used to designate what physical things are made of. The material cause in artistic production is the matter transformed. The formal cause is the form in the artist's mind, which he or she uses when attempting to transform the matter by shaping in one way or another. In other words, the material cause is signate matter -- a potentiality already actualized and thus limited -- that the artist transforms by actualizing the limited potentialities of the matter.
In the process of eating, involving ingestion, digestion, and assimilation, the matter involved is a definite potentiality that is actualized in the process of assimilation by becoming actually like the body of the person who eats the food.
In the process of reproduction, the genetic code contained in the DNA molecule determines all the inherited potentialities of the offspring's body. These are actualized in the process of growth and development.
If I am correct in my theory of the immateriality of the human intellect, it is an actuality rather than a potentiality, and so cannot be genetically determined. Yet intellectual capacities seem to be inherited. This is a mystery.
Adler's Philosophical Dictionary (1995)
Great Ideas from the Great Books (1963)
by Mortimer J. Adler