Losonsky specializes in philosophy of language, metaphysics, and the history of early modern philosophy. He has published in many leading journals, including the Philosophical Review, Philosophical Studies, British Journal of the History of Philosophy, Journal of the History of Philosophy, and Brain and Behavioral Sciences. He is the author of Enlightenment and Action from Descartes to Kant: Passionate Thought (Cambridge University Press, 2001) and Linguistic Turns in Modern Philosophy (Cambridge University Press ,2005). He edited and introduced the critical edition of Wilhelm von Humboldt, On Language (Cambridge University Press, 1999), and a volume of critical essays on Humboldt. He is also coeditor and co-author with Heimir Geirsson of Readings in Language and Mind (Blackwell, 1996) and Beginning Metaphysics (Blackwell, 1998).