I had the idea for writing a book on a priori knowledge from giving a few lectures in a colleague's course on epistemology. I found the available books on a priori knowledge out of date or too difficult for undergraduates. I hope this book is more accessible.

I think the topic of a priori knowledge is a good one to teach to undergraduates. It helps to tie epistemology in with the other subjects that they are taught. It overlaps with ethics (especially with metaethics), logic, philosophy of science and metaphysics. I have tried, especially in the later chapters of this book, to make clear the connections between a priori knowledge and these other fields. Anyone who wishes to follow the radical empiricists and reject a priori knowledge should realize the repercussions for these other fields.

I did not write this book only for students. In it, I try to defend the idea that there is a priori knowledge. Often professional philosophers treat a priori justification as if it were something rather spooky. They associate it with Plato's doctrine of recollection or some sort of extra-sensory perception. My chapter on Aristotelian theories of a priori justification is supposed to help alleviate their fears. Many philosophers also remain suspicious of the analytic–synthetic distinction. There are, however, some good recent defences of analyticity. I try to present them in a manner that is accessible to working philosophers (who may not be epistemologists) as well as to students.