The Knowledge Machine: How Irrationality Created Modern Science

by Michael Strevens

The criminal justice system strives to uncover the truth. Even when it operates as it should, however, its interpretation of the evidence may depend on whether a witness is reliable or a theory—such as the arson investigators’ assumptions about the effect of accelerants—is correct. At the moment when it matters most, there may be no objective basis for answering such questions. Information is limited, yet a determination must be made. The deliberators have no choice but to fall back on what seems most plausible to them. Much later, it may become clear that a witness was untrustworthy or that a theory was flawed. Lacking a crystal ball, the jury must do its best with what it has at the time. It is the same in science. Sometimes it is a measurement instrument—a witness, if you will—on which the issue hinges. Sometimes, it is a theory. Scientists seeking to make sense of the evidence cannot be neutral. They must take a stand on whether the instrument is relaying the truth, on whether the theoretical assumptions hold. Having nothing further to guide them, they must go with whatever seems right. They must resort to educated guesswork, and that makes scientific reasoning irreducibly, unavoidably, essentially subjective.