less known in their nature—namely, by effects." Thomas believed that the existence of God can be demonstrated. Briefly in the Summa Theologiae and more extensively in the Summa contra Gentiles, he considered in great detail five arguments for the existence of God, widely known as the quinque viae (Five Ways). Motion: Some things undoubtedly move, though cannot cause their own motion. Since, as Thomas believed, there can be no infinite chain of causes of motion, there must be a First Mover not moved by anything else, and this is what everyone understands by God. Causation: As in the case of motion, nothing can cause itself, and an infinite chain of causation is impossible, so there must be a First Cause, called God. Existence of necessary and the unnecessary: Our experience includes things certainly existing but apparently unnecessary. Not everything can be unnecessary, for then once there was nothing and there would still be nothing. Therefore, we are compelled to suppose something that exists necessarily, having this necessity only from itself; in fact itself the cause for other things to exist. Gradation: If we can notice a gradation in things in the sense that some things are more hot, good, etc., there must be a superlative that is the truest and noblest thing, and so most fully existing. This then, we call God. Ordered tendencies of nature: A direction of actions to an end is noticed in all bodies following natural laws. Anything without awareness tends to a goal under the guidance of one who is aware. This we call God. Aquinas was receptive to and influenced by Avicenna's Proof of the Truthful. Concerning the nature of God, Thomas, like Avicenna felt the best approach, commonly called the via negativa, is to consider what God is not. This led him to propose five statements about the divine qualities: God is simple, without composition of parts, such as body and soul, or matter and form. God is perfect, lacking nothing. That is, God is distinguished from other beings on account of God's complete actuality. Thomas defined God as the Ipse Actus Essendi subsistens, subsisting act of being. God is infinite. That is, God is not finite in the ways that created beings are physically, intellectually, and emotionally limited. This infinity is to be distinguished from infinity of size and infinity of number. God is immutable, incapable of change on the levels of