In the fourth Way, Aquinas offers a version of the Ontological Argument (see Anselm). In Aquinas’ version some things are noted to exhibit varying degrees of a quality. A thing may be more or less hot, more or less good, more or less noble. Such varying degrees of quality are caused by something that contains the most or perfect amount of that quality. Because, just as the sun is the hottest thing, and thus is the cause of all other things being hot, so there must be some fully ‘good’ thing which makes all other things good. That which is most good is, of course, God.
