A priori knowledge of the way the world works

Abstract

Science is last place one might expect to find thought experiments. Thought experiments happen entirely in our minds, but science is supposed to tell us about how the world works. So how can something that happens entirely in our minds give us reason to believe anything about the nature of the world? This is the philosophical puzzle at the heart of James Robert Brown’s classic, The Laboratory of the Mind, now in its second edition. With two new chapters and extensive additions to two others, the single best introduction to the philosophical issues raised by thought experiments in science has just gotten better. Brown’s book can be usefully divided into three parts. Chapters 1–3 set forth the raw evidence that any theory of thought experiments must explain. These chapters introduce many examples of thought experiments and attempt to organize them in terms of how they work in science. Chapters 4 and 5 make the case for scientific Platonism. For Brown, thought experiments in science are successful because we are capable of acquiring a priori knowledge of the way the world works. Laws of nature are abstract objects that we have some sort of cognitive access to. The last three chapters, 6–8, display the power of Brown’s Platonism by applying it to scientific practice. This review will focus primarily on the first two parts of the book. The opening chapter offers a clear, patient and extremely valuable introduction to over a dozen important thought experiments. Chapters 2 and 3 set forth a perspicacious framework that taxonomizes thought experiments in terms of how they work epistemically in science. To understand the core of this taxonomy, it will be useful to begin with Brown’s favorite thought experiment. Galileo on Free Fall: Suppose, we attach a heavy cannon ball to a light musket ball and release them from a tower. If heavier bodies fall faster than lighter bodies, then the musket ball should