In this episode Harland engages in some more of that pesky normative semantics and proposes a new definition of the word 'definition' (n): a paraphrastic replacement function. Huh? Well then he defines all those words too!
The primary intent is to provide a pragmatically, anthropologically useful interpretation of current usage while not relying on a putatively unsupportable definition that includes notions like 'meaning' or 'speaker intentions', or other conceptual frameworks that Harland doesn't like.
Instead it hopes to accord smoothly with physicalism and functionalism, which the Dawds suspect are probably the best models we have available at this time. Let's try to bring philosophy of language into closer consilience with the rest of our intellectual edifice!