Causation and Modality: Models and Meanings
Dean McHugh

Abstract:
This thesis aims to answer two questions about causal claims (such as sentences containing ‘cause’ or ‘because’). Firstly, the modelling question: what kind of information do we use when we judge that a causal claim holds? Secondly, the meaning question: under what conditions do we judge that a causal claim is true?

Our answer to the modelling question is that a causal model must contain time, part–whole structure, and nomic possibility. The model represents scenarios as extended in time, with each moment in time having a mereological structure (the mereological structure tell us, for example, that the state of Amsterdam is part the state of the Netherlands). The notion of nomic possibility specifies which worlds are nomically possible and which worlds are nomically impossible; in other words, which worlds satisfy the laws and which do not. In addition, the model must also contain two language-related components. For each sentence, the model must tell us what parts of the world it is about, and in which worlds the sentence is true. 

We show that this this modelling framework is strictly more general than a popular alternative, that of structural causal models. Every structural causal model can be represented into our framework, and therefore every scenario that structural causal models can represent our framework can represent too. However, the converse does not hold. There are some scenarios that our proposed model can represent which structural causal models cannot.

We use these components to analyse how people construct hypothetical alternatives to reality. For it is commonly thought that the truth of a causal claim depends not only on what goes on in the actual world, but on what happens in some hypothetical scenarios as well. For example, when we evaluate “Alice missed her flight because she got stuck in traffic” we imagine scenarios where she is stuck in traffic and scenarios where she is not, and compare what happens in each. 

We then analyse the semantics of ‘cause’ and ‘because’ in terms of two relations: sufficiency and production. The meaning of ‘cause’ and ‘because’ is a blend of these relations: ‘C cause E’ and ‘E because C’ are true just in case C is true, and C is sufficient to produce E but C's negation is not.