The whole explanation, part by part.

We can often explain properties of a whole in terms of its parts. For example, an aeroplane’s ability to fly can be explained by the fact that it has wings. Such part–whole explanations presuppose a mereological structure, i.e., a formal theory about the part–whole relation. Yet, despite the growing interest in such explanations, there is currently no metaphysical account of this mereological structure. This project explicates this mereological structure using a counterfactual analysis. This analysis starts with the idea that to say that a specific part explains a property of the whole means that if the whole were lacking that part, then it would lack the relevant property, too. For example, if an aeroplane lacked wings, then it would also lack the ability to fly; hence the wings help explain the aeroplane’s ability to fly. Counterfactual analyses are used by philosophers to explain the success of causal explanations, while part–whole explanations are a prime example of non-causal explanations. The project thus synthesizes two lines of philosophical research and makes the rich counterfactual theories about causal reasoning available for explicating a form of non-causal reasoning. This bridge between causal and non-causal explanations greatly increases our understanding of explanation in general. The project results in a part–whole theory that is expressed in a formal language that contains modal notions—such as necessarily and possibly—and a similarity relation. This augmented modal mereology constitutes a detailed and original metaphysical theory about part–whole explanations which details the conditions under which such explanations are successful. The project thereby not only contributes to the study of non-causal explanations within analytic metaphysics but also provides a fruitful addition to the formal frameworks that are used by information scientists to systematize datasets, especially in the field of bio-information.