Reason without much language
Language is more than a system used for interpersonal communication. Linguistic representations can also form a part of reasoning in other cognitive domains. However, it is unclear whether the role of language in non-verbal domains is a necessary one, or whether it represents an optional resource that is recruited under demanding or highly intentional processing conditions. The possible role of language in categorisation, belief reasoning, calculation and cross-domain integration is explored, together with the various sources of evidence that can inform debates on language–thought relationships. Evidence from comparative and developmental psychology, together with that from neuroscience and ‘virtual language impairment’ (verbal shadowing) suggests reduced or absent language resource can disrupt performance in non-verbal domains. Similarly results of some investigations of people with developmental or acquired language impairments suggest an association with broader cognitive impairment. However, there is a substantial and growing body of evidence from across experimental fields indicating autonomy between language and reasoning. Residual reasoning in the face of severe aphasia is described, together with possible objections to the evidence from aphasia informing language and thought debates.