Aristotle gives form priority over matter

REALITY. Metaphysics
St. Thomas is in part the thought of Aristotle, but not limited to accept its teachings without more, but extends them in some places and modifies others.

St. Thomas took the Aristotelian distinction between matter and form, between substance and accident, and between power and act, though the latter gives a new meaning.

Still, the more important is that referring to the analogy of being, which is based on what the body is the essence and the act of being (esse) of that essence.

That comes to a new theory that distinguishes and describes two types of substances, the material entities that are accessible through the senses and that is ontologically divided between the substantial level, where matter is related to the form, as the power to act , where matter is indeterminate and shape gives it its essential determination, come on, what makes the matter be that thing or another. However, this essence is only power being in relation to the act of being. The other level is the accidental, since, although the substance is determined by the accidents, which make him accidentally in one way or another. Hence, they call them accidents are accidental forms or acts seconds.

Within immaterial substances, are als remaining pure forms or as angels or demons. For Aquinas, these separate substances are composed of potency and act, like other creatures, but at a level that is not hilermórfico because its essence is lacking in substance and matter, but as with the material substances, is also distinguishable from the act of being (esse).

God created beings possess an essence that is the power of being and who is not his own act of being, but to God this is not applicable, because that is to be subsistent act of being pure in essence. He is being as identity, whereas creatures are inidénticas. Since for part of Sto Tomas beings in the world, known by the senses, and from them, makes his metaphysical analysis.

Being an act is exercised by the material realities of living and, in a more perfect, immaterial substances.

Also, being as creatures have borrowed, as none of them appropriates be such that it has the essence, only God is being by essence. Compared with God, everything else in quota. Thus the necessary being is one in essence identified by the act of being, while the quota is that in its essence does not include the act of being.