Locke’s semantics is especially vulnerable to a private language argument. For him words stand for ideas and meanings are ideas themselves. Ideas are either private objects of experience or composed of these. How can then language serve as a means of communication? Although Locke faces the problem, his answer to the question, as I’ll argue, falls short of being satisfactory, and consequently it may seem that empiricist semantics, as it stands, is inevitably trapped by a private conception of language. However, it is possible to refine this theory of meaning by addition of conventions. I’ll extend Hume’s theory of conventions to semantics, arguing that this extension is not arbitrary on the one hand, and can save empiricists from the burden of private language.