This paper deals with the relation between our means of acquiring knowledge and our understanding of physical reality: between epistemology and the physical sciences. Science relies, whether explicitly or implicitly, on certain premises about how knowledge can be acquired and verified. If those premises are correct, a scientist is limited only by his own ambition and resources in what truths of nature he might uncover. But if those premises are wrong, the scientist’s investigations are needlessly hampered, like an astronomer who knows no better than to make all his observations in daylight. What are the crucial epistemological principles that serve as a foundation to the physical sciences? How does the way we “do” science rely on these fundamental premises? What are the consequences of holding the wrong premises, and how have such errors affected the development of the physical sciences?