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 H2O, then water is identical to H2O – thus we get unity. Unity does not come at the price of elimination – claiming that water reduces to H2O, 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 H2O, such that we get diversity. This is required for there to be directionality: in a sense, if water reduces to H2O, then H2O is prior to, or more basic than water. At least, if water reduces to H2O, then H2O does not reduce to water. But how can this be, if water is identical to H2O? 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.