This article is on Aristotelian and Neo-Aristotelian definitions of God.
In his book on first philosophy, which most now call the Metaphysics, Aristotle discussed the meaning of "being as being". Some see contradictions in this book, and conclude that it puts together many different works that Aristotle wrote at different times. Others find a coherent argument in the book. According to the latter reading, Aristotle concluded that "being" primarily refers to the Unmoved Movers, and assigned one of these to each movement in the heavens. In the Aristotelian theory each Unmoved Mover continuously contemplates its own contemplation, and everything that fits the second meaning of "being" by having its source of motion in itself, moves because the knowledge of its Mover causes it to emulate this Mover (or should).
This influenced Anselm's view of God, who he called "that than which no greater being can be conceived". Anselm thought that God did not feel emotion such as anger or love, but appeared to do so through our imperfect understanding. The incongruity of judging "being" against something that might not exist may have led Anselm to think that he had proved God's existence.
Many medieval philosophers made use of the idea of approaching a knowledge of God through negative attributes. For example, we should not say that God exists in the usual sense of the term; all we can safely say is that God is not nonexistent. We should not say that God is wise, but we can say that God is not ignorant, i.e. in some way God has some properties of knowledge. We should not say that God is One, but we can state that there is no multiplicity in God's being. See apophatic theology.
Aristotle devotes special attention to the Platonic theory, according to which ideas are the ultimate principles of Being. That theory, he contends was introduced to explain how things are, and how things are known; in both respects, it is inadequate. To postulate the existence of ideas apart from things is merely to complicate the problem; for, unless the ideas have some definite contact with things, they cannot explain how things came to be, or how they came to be known by us. Plato does not maintain in a definite, scientific way a contact between ideas and phenomena -- he merely takes refuge in expressions, such as participation, imitation, which, if they are anything more than empty metaphors, imply a contradiction. In a word, Aristotle believes that Plato, by constituting ideas in a world separate from the world of phenomena, precluded the possibility of solving by means of ideas the problem of the ultimate nature of reality.
What, then, are, according to Aristotle, the principles of Being? In the metaphysical order, the highest determinations of Being are Actuality (entelecheia) and Potentiality (dynamis). The former is perfection, realization, fullness of Being; the latter imperfection, incompleteness, perfectibility. The former is the determining, the latter the determinable principle. Actuality and potentiality are above all the Categories; they are found in all beings, with the exception of the Supreme Cause, in Whom there is no imperfection, and, therefore, no potentiality. God is all actuality, Actus Purus. All other beings are composed of actuality and potentiality, a dualism which is a general metaphysical formula for the dualism of matter and form, body and soul, substance and accident, the soul and its faculties, passive and active intellect. In the physical order, potentiality and actuality become Matter and Form. To these are to be added the Agent (Efficient Cause) and the End (Final Cause); but as the efficiency and finality are to be reduced, in ultimate analysis, to Form, we have in the physical order two ultimate principles of Being, namely, Matter and Form. The four generic causes -- Material, Formal, Efficient, and Final -- are seen in the case, for instance, of a statue:
- The Material Cause, that out of which the statue is made, is the marble or bronze.
- The Formal Cause, that according to which the statue is made, is the idea existing in the first place as exemplar in the mind of the sculptor, and in the second place as intrinsic, determining cause, embodied in the matter.
- The Efficient Cause, or Agent, is the sculptor.
- The Final Cause is that for the sake of which (as, for instance, the price paid the sculptor, the desire to please a patron, etc.) the statue is made.
In the "Metaphysics" he takes the stand that the actual is of its nature antecedent to the potential, that consequently, before all matter, and all composition of matter and form, of potentiality and actuality, there must have existed a Being Who is pure actuality, and Whose life is self-contemplative thought (noesis noeseos). The Supreme Being imparted movement to the universe by moving the First Heaven, the movement, however, emanated from the First Cause as desirable; in other words, the First Heaven, attracted by the desirability of the Supreme Being "as the soul is attracted by beauty", was set in motion, and imparted its motion to the lower spheres and thus, ultimately, to our terrestrial world. According to this theory God never leaves the eternal repose in which His blessedness consists. Will and intellect are incompatible with the eternal unchangeableness of His being. Since matter, motion, and time are eternal, the world is eternal. Yet, it is caused. The manner in which the world originated is not defined in Aristotle's philosophy. It seems hazardous to say that he taught the doctrine of Creation. This much, however, may safely be said: He lays down principles which, if carried to their logical conclusion, would lead to the doctrine that the world was made out of nothing or always existed.
Aristotelian theology was accepted by many later Jewish philosophers, such as Maimonides, Gersonides, Samuel Ibn Tibbon and many others; their views of God are considered mainstream by many Jews of all denominations even today. Aristotelian theology was also accepted by many later Christian and Islamic philosophers and theologians in the medieval era, notably Thomas Aquinas.