The fourth of the Five Ways of Aquinas. Its premises include: (i) some things are better and more noble than others; (ii) comparative terms describe varying degrees of approximation to a superlative; (iii) whatever is the best is the most fully in being, or most real; (iv) whenever things possess some property in common, the one most fully possessing it causes it in the others. Hence, there is something which ‘causes in all other things their being, their goodness and whatever other perfections they have. And this we call God.’ The argument presupposes a concept of causation as a kind of gift of reality. This idea survived until the 17th century, but is no longer attractive. In addition, the second premise is clearly faulty (one number may be greater than another, but there is no greatest number; similarly one automobile may be better than another without there being a perfect automobile). In so far as the argument depends upon an association of value with degrees of reality, and thence with causation, it is probably best seen as a version of the cosmological argument.