 There has been increasing attention in epistemology to thick epistemic concepts such as gullible, quick to jump to conclusions, and open-minded. This is particularly common in virtue epistemology, which seeks to explain epistemic properties such as knowledge and justified belief in terms of the cognizer’s intellectual virtues and vices. Whether focusing on thick epistemic concepts can lead to a preferable epistemology is the topic of several papers in a special issue of the journal Philosophical Papers (Kotzee and Wanderer 2008; see also Battaly 2001). A foundational question here is whether there is a distinction between thick and thin epistemic concepts and whether it be understood in the same way as the distinction between thick and thin ethical concepts (Väyrynen 2008; Roberts 2018a). For instance, are thick epistemic concepts supposed to be thick in the sense that they involve evaluation and non-evaluative description, or in the sense that they involve epistemic and non-epistemic content? (These are different distinctions even if epistemic content is often evaluative and non-epistemic content often non-evaluative.) These discussions almost invariably assume that knowledge is a thin concept. But Brent Kyle argues that knowledge is better understood as a thick concept and uses its thickness to cast light on why the so-called Gettier problem for definitions of knowledge arises (Kyle 2013b).