The Concept of Reduction

The book takes its point of departure in the examination of a puzzle about reduction. To illustrate, the book takes as an example the reduction of water. If water reduces to H O, then water is identical to H O – thus we get unity. Unity does not come at the price of elimination – claiming that water reduces to H O, we do not thereby claim that there is no water. But what about diversity and directionality? Intuitively, there should be a difference between water and H O, such that we get diversity. This is required for there to be directionality: in a sense, if water reduces to H O, then H O is prior to, or more basic than water. At least, if water reduces to H O does not reduce to water. But how can this be, if water is identical to H O? The book shows that the application of current models of reduction does not solve this puzzle, and proposes a new coherent definition, according to which unity is tied to identity, diversity is descriptive in nature, and directionality is the directionality of explanation.