Was Heidegger an externalist?

To address the question posed in the title, I focus on Heidegger's conception of linguistic communication developed in the sections on Rede and Gerede of Being and Time. On the basis of a detailed analysis of these sections I argue that Heidegger was a social externalist but semantic internalist. To make this claim, however, I first need to clarify some key points that have led critics to assume Heidegger's commitment to social externalism automatically commits him to semantic externalism regarding concept use. I begin by explaining the independence of those positions, arguing that social externalism answers the question of whose concepts in a linguistic community are properly individuated, whereas semantic externalism makes a claim about what it takes for concepts to be properly individuated. Once these issues are distinguished, it is possible to see that Heidegger's intersubjectivist conception of language commits him to social externalism, while his conception of the ontological difference commits him to semantic internalism.