Locke on Hypotheses: A Via Media

Patrick j. Connolly

Iowa State University

In this paper I examine John Locke’s views on the proper role and status of hypotheses in natural philosophy. Locke’s texts display a markedly mixed attitude toward hypotheses. Sometimes he is disparaging: “tis but ostentation & losse of time to lay down hypothesis wch are many times false [and] always uncertain.” At other times, however, he speaks highly of them: “The way to finde truth as far as we are able to reach it … is to pursue the hypothesis that seems to us to carry with it the most light & consistency...” As a result, some commentators have argued that Locke embraced hypotheses and saw them as the cornerstone of natural philosophical theory and practice (Soles, Mandelbaum, Woolhouse, Laudan, Farr). Others, however, have argued that Locke either rejected hypotheses completely or thought they should play only a minimal role in natural philosophical enquiry (Anstey, Ducheyne, Walmsley, Yost, Yolton). In this paper I develop an interpretation of Locke on hypotheses which seeks to make sense of the mixed attitude found in his texts. More specifically, I argue that Locke accepted hypotheses in natural philosophy provided they were of the right kind. So rather than argue, as previous commentators have done, that Locke either accepted or rejected natural philosophical hypotheses wholesale I argue that his attitude was more nuanced. Locke rejected some hypotheses and accepted others for use in natural philosophy. He thought that only certain hypotheses would be suitable for helping natural philosophers make predictions, design experiments, formulate theories, and explain phenomena. But which hypotheses did Locke think were acceptable? And why? Locke believed a hypothesis needed to meet five criteria in order to be acceptable for use in natural philosophy: 1) It must be formed cautiously. A certain kind of caution was required to avoid a number of psychological biases which Locke believed humans were susceptible to. 2) It must only employ terms with fixed and determined meanings. Verbal precision and consistency was required in formulating hypotheses to avoid confusion. 3) It must remain neutral on the nature of substance. For Locke, the true nature of material substance was beyond our ken, so our hypotheses must not commit us to any particular view. 4) It must not invoke a real essence. Locke believed that we were entirely ignorant of the real essences of bodies, so we cannot appeal to them in natural philosophy. 5) It must be formulated on the basis of careful observation and it must conform to all previously observed phenomena. I examine the role that these criteria play in Locke’s own experiments and statements about natural philosophy. And I also show that he used a failure to meet these criteria as a way to disparage the hypotheses of his opponents in natural philosophy (Cartesians, Scholastics, and Paracelsians). Finally, I examine how Locke’s criteria for an acceptable hypothesis closely parallel those of his natural philosophical associates (especially Boyle and other members of the Royal Society).