The Ordinary Language Movement in 20th century philosophy is typically associated with the work of the later Wittgenstein, Ryle, Austin, and, to some extent, Strawson. 2 The movement was massively influential, but today it's unusual to find philosophers self-ascribing that label. In some circles, the label 'ordinary language philosophy' is slightly derogatory-an indication that the work is somewhat outdated and methodologically flawed. In this paper, we want to counteract that attitude. Some of the core ideas behind the movement are and should be central to work done in all parts of philosophy. We try to articulate how and why ordinary concepts are central to much of philosophy (in a way that they are not to, say, physics). We develop our positive view by responding to some anti-ordinary language arguments found in David Chalmers' paper "Verbal Disputes" (Chalmers 2011). We then contrast our positive view of the role of language in philosophy, with that found in Timothy Williamson's The Philosophy of Philosophy (Williamson 2007).When Ordinary Language Does and Doesn't Matter 1 Thanks to three anonymous reviewers at this journal for helpful comments. 2 The seminal texts in the tradition include Austin 1962, some of Ryle's papers (1971), and perhaps Strawson's work on 'descriptive' metaphysics (1959). For an overview, see Parker-Ryan nd. Relevant also is the so-called 'contemporary' ordinary language philosophy (Hansen 2014;2018;2020). This includes work in experimental philosophy, but also mainstream subdisciplines of contemporary philosophy, including ones discussed below. One way to view this paper is as exploring the foundations of contemporary ordinary language philosophy.We'll start with some paradigms of inquiries where ordinary, non-theoretic notions plays no significant role: Doesn't matter: Physicists study mass and in so doing, they don't care about the ordinary notion of 'mass' or how ordinary speakers of English use the expression 'mass'. Biologists who study genes don't care about the ordinary notion of 'gene'. Economists who study inflation don't care much about the ordinary notion of 'inflation. When doctors study cancer, the last thing they need to think about is the ordinary notion of 'cancer'. Mathematicians and logicians don't care about facts about how ordinary speakers use the word 'infinite'. In all these cases, there's an entrenched theoretical notion that's well defined within the respective disciplines.With that in mind, why should philosophers care about the ordinary notions of knowledge, or freedom or goodness? Why don't they just introduce new technical terms, in the way these scientific disciplines do, and leave behind the English words 'knows', 'free' and 'good'?In many parts of philosophy there is a deep deference to and focus on the ordinary concept, with an accompanying interest in the lexical item that expresses that concept. This paper is an effort to explain why and to defend that strategy. Before we get to the normative point -that deference to the ordinary is a good thing -...