The main question discussed in current debates about the epistemology of testimony concerns whether the justification of testimonial beliefs is inferential or non-inferential. This thesis offers a novel argument for inferentialism, the former view. It does so through, firstly, assuming a widely shared view about the psychology of comprehension – the inferential model of communication – along with widely shared views about the epistemic basing relation and inferential justification, and then, secondly, arguing that inferentialism in the epistemology of comprehension - the view that (i) comprehension states are beliefs, and (ii) that the justification of such states is inferential - follows from these assumptions. It is then argued that inferentialism in the epistemology of testimony follows from inferentialism in the epistemology of comprehension. Through offering this argument, the thesis aims to demonstrate that our views about the psychology of comprehension have far-reaching consequences for our theorizing in the fields of epistemology of testimony and epistemology of comprehension. In fact, widely held such views arguably have as a consequence that neither testimony nor comprehension are sources of non-inferential justification, an important epistemological insight.