Becker’s Rule is Not Becker’s Rule

The name “Becker’s rule” was coined by C. West Churchman in 1938 to denote the modal inference rule according to which the theoremhood of a strict implication of the form   may be inferred from the theoremhood of a strict implication of the form . According to Churchman, such a rule was introduced explicitly by Oskar Becker in his On the Logic of Modalities (1930)—hence the name he gave to it, which is still current in the literature. The aim of this note is to point out that “Becker’s rule” is not at all Becker’s rule (a fact which has remained unnoticed until now, as far as we know) by explaining where and how Churchman misunderstood what Becker intended.