Why is science fallible? Scientific investigation aims to disclose the general principles that govern the workings of the universe. There principles are not intended merely to summarize what some select groups of humans have witnessed. Natural science is not just natural history. It is vastly more ambitious. Science offers us laws that are supposed to hold universally, and it advances claims about things that are beyond our power to observe. The nuclear physicist who sets down the law governing a particular type of radioactive decay is attempting to state a truth that holds throughout the entire cosmos an also to describe the behavior of thing that we cannot even see. Yet, of necessity, the physicist’s ultimate evidence is highly restricted. Like the rest of us, scientists are confined to a relatively small region of space and time and equipped with limited and imperfect senses. How is science possible al all? How are we able to have any confidence about the distant regions of the cosmos and the invisible realm that lies behind the surfaces of ordinary things? The answer is complicated. Natural science follows intricate and intricate and ingenious procedures for fathoming the secrets of the universe. Scientists devise ways of obtaining especially revealing evidence. They single out some the things we are able to see as crucial clues to the way that nature works. These clues used to answer questions that cannot be addressed by direct observation. Scientific theories, even those that are most respected and most successful, rest on indirect arguments from the observational evidence. New discoveries can always call those arguments into question, showing scientists that the observed data should be understood in a different way, that they have misread their evidence.