The author attempts to show that scientific realism is compatible with the presence of idealization in the sciences. His main contention is that idealized theories can be treated as counterfactuals about how things are in worlds that are similar to but simpler than the actual world.

The author attempts to show that scientific realism is compatible with the presence of idealization in the sciences. His main contention is that idealized theories can be treated as counterfactuals about how things are in worlds that are similar to but simpler than the actual world.

Before the 20th century, the concept of a priori knowledge -- knowledge based in reason and reflection rather than experience -- found nearly universal acceptance. By the early 20th century, however, philosophers were skeptical of the idea that there was any nontrivial existence of a priori knowledge. Fifty years later, it was fashionable to doubt it existed at all. The articles in this book tackle a priori knowledge from every angle -- does it exist? what might it be like? what is its relation to empirical knowledge? -- and other topics of perennial interest.