This is one of the most convincing philosophy books I have read in a long time. It takes a widely held constellation of views, lays them out with admirable clarity, and patiently reduces them to rubble. (Jeff Speaks, University of Notre Dame)

It is natural to distinguish, for any thinking creature, those events and states that are internal to the creature ? its brain states, for example ? from those that are not. Narrow mental content, if there is such a thing, is content that is entirely determined by the goings-on inside the head of the thinker. A central question in the philosophy of mind since the mid-1970s has been whether there is a kind of mental content that is narrow in this sense. One important line of thought ? by 'externalists' ? has been that so-called intentional states, such as wishing that they sky were blue and believing that the sky is blue, are, perhaps surprisingly, not internal: there could be twins who are exactly alike on the inside but differ with respect to such intentional states. In the face of this wave of externalism, many philosophers have argued that there must be some good sense in which our intentional states are internal after all, and that such narrow content can play various key explanatory roles relating, inter alia, to epistemology and the explanation of action. This book argues that this is a forlorn hope, and defends a thoroughgoing externalism. The entanglement of our minds with the external world runs so deep that no internal component of mentality can easily be cordoned off.

Juhani Yli-Vakkuri is Professor in Philosophy of Language at the University of Tartu and Alexander von Humboldt Research Fellow at the University of Bielefeld, having previously been Postdoctoral Research Fellow at the Centre for the Study of Mind in Nature (CSMN), University of Oslo. He is the author of several papers in the philosophy of language, the philosophy of mind, epistemology, and philosophical logic, as well as co-editor, with Mark McCullagh, of Williamson on Modality (Routledge, 2017).

John Hawthorne is Professor of Philosophy at the University of Southern California, and a Fellow of the British Academy. He was previously Waynflete Professor of Metaphysical Philosophy at the University of Oxford and Professor of Philosophy at Rutgers, the State University of New Jersey. His books include Knowledge and Lotteries (OUP 2004), Metaphysical Essays (OUP 2006), Relativism and Monadic Truth (OUP 2009, with Herman Cappelen), and The Reference Book (OUP 2012, with David Manley).