The paper defends two assumptions in Burge's externalist argument against materialism. One assumption is that the content of a belief is determined by the rules that govern its expression in a shared language. Hence, I call this principle linguistic socialism. According to the other assumption, a belief survives as long as it keeps its content. Content is regarded here as essential to a belief, so I call this principle semantic essentialism. The critics of socialism such as Davidson and Bilgrami reject it in favour of individualism, claiming that mental content is independent of conventionally fixed meaning. The opponents of essentialism such as Gibbons prefer accidentalism, arguing that content is inessential to a belief. I argue that individualism and accidentalism contradict empirical facts and modal intuitions about belief ascription, respectively.