This article makes a case that disability, particularly visual, hearing, and speech impairments, played a significant role in Scottish Enlightenment thought. Focusing on the work of Dugald Stewart, and in particular on his essay ‘Some account of a boy born blind and deaf’, we argue that disability was a deep preoccupation of Scottish Enlightenment thinkers who used it as a test case for various important philosophical questions including those concerning ‘human nature’ and the limits of humanity. The article starts by situating the philosophical debate in the context of lived experiences of, and proximity to, impairment. The second part offers a close reading of Stewart's text ‘Some account’, about James Mitchell, a fourteen-year-old deafblind boy living in the Scottish Highlands. The third part examines how disability operated in relation to other hierarchies of difference that have been demonstrated to have been central to Enlightenment thought, in particular that of race. Overall, the contribution this article makes is to introduce disability as an important, if currently overlooked, category in Scottish Enlightenment thought that needs further investigation.