Enthymemetic Conditionals

Proceedings of the Eighth Joint Conference on Lexical and Computational Semantics (*SEM), pages 168–177 Minneapolis, June 6–7, 2019. c⃝2019 Association for Computational Linguistics 168 Enthymemetic Conditionals: Topoi as a guide for acceptability Eimear Maguire Laboratoire Linguistique Formelle (UMR 7110), Universit´e de Paris eimear.maguire@etu.univ-paris-diderot.fr Abstract To model conditionals in a way that reflects their acceptability, we must include some means of making judgements about whether antecedent and consequent are meaningfully related or not. Enthymemes are non-logical ar- guments which do not hold up by themselves, but are acceptable through their relation to a topos, an already-known general principle or pattern for reasoning. This paper uses en- thymemes and topoi as a way to model the world-knowledge behind these judgements. In doing so, it provides a reformalisation (in TTR) of enthymemes and topoi as networks rather than functions, and information state update rules for conditionals. 1 Introduction The content of the antecedent and consequent of a conditional, not just their truth or falsity, makes a difference to whether we find the conditional ac- ceptable or not, generally rejecting those that seem disconnected (Douven, 2008). If we are to model conditionals in a way that reflects their acceptabil- ity, we must include some means of making those judgements. Enthymemes are non-logical argu- ments which do not hold up by themselves, but are acceptable through their relation to a topos, an already-known general principle or pattern for reasoning. Arguments and justifications in inter- action tend to be underpinned by general princi- ples and rules of thumb, rather than being truly ‘logical’. For models of dialogue to be adequate then, these non-logical arguments need to be han- dled – namely, as proposed by Breitholtz (2014a), through incorporating enthymemes and topoi into the dialogue model. Apart from the evidence from their own acceptability conditions, which corre- late strongly with judgements of high conditional probability, conditional structures are also asso- ciated with ‘that kind of thinking’, being used as plain-language explanations of particular topoi (e.g. “if something is a bird, then it flies” in Bre- itholtz, 2014b), or used as materials on reasoning in any number of experiments (e.g. Pijnacker et al., 2009). If we are going to explicitly recognise the use of such ‘rule’ type objects in discourse, then conditionals are one place where they show up, at least sometimes. This paper has two aims. First, to propose a for- malisation of enthymemes and topoi that is geared towards relating them to more complex rule-based world knowledge, including a distinction between knowledge about causality, non-causality, and am- biguity about causality. Second, to account for the acceptability (or not) of conditionals by proposing an enthymeme-like structure as associated with if-conditionals, such that topoi can enhance their content and are used in judging whether a given conditional is acceptable or not. The acceptabil- ity of conditionals is linked to perceived rela- tionships between the antecedent and consequent cases: with enthymemes and topoi, whose pres- ence in the model is independently justified, we can incorporate this non-arbitrarily into the …

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