Abstract: How is knowledge of the external world possible? How is knowledge of other minds possible? How is a priori knowledge possible? These are all examples of ‘how-possible’ questions in epistemology. In general, we ask how knowledge, or knowledge of some specific kind, is possible when we encounter obstacles to its existence or acquisition. So the question is: how is knowledge possible given the various factors that make it look impossible? A satisfactory answer to such a question will therefore need to do several different things. In essence, explaining how a particular kind of knowledge is possible is a matter of identifying ways of acquiring it, overcoming or dissipating obstacles to its acquisition, and figuring out what makes it possible to acquire it. To respond to a how-possible question in this way is to go in for what might be called a ‘multi-levels’ approach. The aim of this book is to develop and defend this approach.

Keywords: how-possible questions, acquiring knowledge, a priori knowledge, external world knowledge, other minds