Dean McHugh

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.

This paper is concerned with disjunctions of universal modals, such as ‘You have to clean your room or you have to walk the dog’, and disjunctions of conditionals, such as ‘If Alice dances, Charlie will dance, or if Bob dances, Charlie will dance’. We aim to provide a uniform account of their surprising behaviour. Our proposal combines three independently attested components. Firstly, disjunction's dynamic effect, familiar from presupposition projection: when we evaluate a disjunction ‘A or B’, we typically interpret B assuming the negation of A, and optionally, also interpret A assuming the negation of B. Secondly, the fact that disjunctions often receive a conjunctive interpretation, familiar from free choice phenomena. Thirdly, that modal bases are restricted to local contexts, what Mandelkern has called ‘bounded modality’.

The similarity approach to conditionals (Stalnaker 1968; Lewis 1973) predicts Reciprocity to be valid: whenever A > B, B > A and A > C are true, B > C is true too (where A > B denotes if A would B). We ran an experiment to test the validity of this rule. Strikingly, half of our participants judged the rule invalid, i.e. judged in at least one scenario that it does not preserve truth. Our data also challenge Kratzer’s (2012) and Fine’s (2012) semantics of conditionals, but we show that McHugh’s (2022; 2023) aboutness approach can account for our data.

In this paper I would like to offer a new framework for hypothetical reasoning, with the goal of predicting what scenarios we consider when we interpret a conditional or causal claim (such as a sentence containing the word ‘because‘). The idea is that when we interpret a conditional or causal claim, we identify a part of the world to change and imagine changing that. Sentences are about parts of the world: when we interpret a conditional antecedent or because clause, we allow the part of the world it is about to vary. My main evidence for this approach is that it gives just the right range of hypothetical scenarios to account for how we interpret both conditionals and causal claims. Some approaches (such as Stalnaker and Lewis’s semantics of conditionals based on similarity, and Kratzer’s premise semantics) consider too few scenarios, while others (such as Fine’s truthmaker semantics of conditionals) consider too many. The present approach inhabits a Goldilocks zone between these extremes: not too restrictive, not too permissive, but just right.