Locke’s Knowledge of Ideas: Propositional or By Acquaintance?

Locke seems to have conflicting commitments: we know individual ideas and all knowledge is propositional. This paper shows the conflict to be only apparent. Looking at Locke’s philosophy of language in relation to the Port Royal logic, I argue, first, that Locke allows that we have non-ideational mental content that is signified only at the linguistic level. Second, I argue that this non-ideational content plays a role in what we know when we know an idea. As a result, we can see our knowledge of an idea as a form of knowledge by acquaintance: there is a direct epistemic relation between a mental object and a knowing subject. But owing to Locke’s logic, that knowledge has a tacit propositional structure expressing the truth of the idea, which gains full signification only linguistically.