Sometimes ordinary disagreements become deep as a result of epistemic injustice. The paper explores a hitherto unnoticed connection between two phenomena that have received ample attention in recent social epistemology: deep disagreement and epistemic injustice. When (pre-existing) epistemic injustice comes into play in a regular disagreement, this can lead to higher-order disagreement about what counts as evidence concerning the original disagreement, which deepens the disagreement. After considering a common definition of deep disagreement, it is proposed that the depth of disagreements is best understood as a matter of degree. Then, a case study of real-life disagreement is introduced: the disagreement about whether racism is a significant issue in the Netherlands, illustrated by the tradition of ‘Black Pete’. It is argued that there is disagreement about what counts as evidence in the case study because of two forms of epistemic injustice: testimonial and hermeneutical injustice. Specifically, there is disagreement about (the application of) epistemic principles concerning (A) whether private first-personal experience of racism is a weighty source of evidence in this domain, (B) whether victims of racism count as important testifiers in this domain, and (C) how to assess testimony that is not (fully) intelligible to you because it employs concepts and terminology you are unfamiliar with. By dismissing the relevant testimony and epistemic resources, the disagreement boils down to disagreement on the level of epistemic principles concerning (A), (B), and (C). Introducing injustice-based deep disagreement highlights moral and political aspects of disagreements that might seem factual.

Some disagreements concern our most fundamental beliefs, principles, values, or worldviews, such as those about the existence of God, society and politics, or the trustworthiness of science. These are 'deep disagreements'. But what exactly are deep disagreements? This paper critically overviews theories of deep disagreement. It does three things. First, it explains the differences between deep and other kinds of disagreement, including peer, persistent, and widespread disagreement. Second, it critically overviews two mainstream theories of deep disagreement, the Wittgensteinian account and the Fundamental Epistemic Principle account, before introducing a Hybrid account. Finally, it explores the notion that deep disagreements can be deeper than others.

What is the epistemological significance of deep disagreement? Part I explored the nature of deep disagreement, while Part II considers its epistemological significance. It focuses on two core problems: the incommensurability and the rational resolvability problems. We critically survey key responses to these challenges, before raising worries for a variety of responses to them, including skeptical, relativist, and absolutist responses to the incommensurability problem, and to certain steadfast and conciliatory responses to the rational resolvability problem. We then pivot to the ethical and political dimensions of deep disagreement. We focus on whether an unwillingness to engage with positions one considers to be immoral or repugnant might be good, and conclude with some reflections on the moral risks of engagement.