‘Morgan's canon’ is a rule for making inferences from animal behaviour about animal minds, proposed in 1892 by the Bristol geologist and zoologist C. Lloyd Morgan, and celebrated for promoting scepticism about the reasoning powers of animals. Here I offer a new account of the origins and early career of the canon. Built into the canon, I argue, is the doctrine of the Oxford philologist F. Max Müller that animals, lacking language, necessarily lack reason. Restoring the Müllerian origins of the canon in turn illuminates a number of changes in Morgan's position between 1892 and 1894. I explain these changes as responses to the work of the American naturalist R. L. Garner. Where Morgan had a rule for interpreting experiments with animals, Garner had an instrument for doing them: the Edison cylinder phonograph. Using the phonograph, Garner claimed to provide experimental proof that animals indeed spoke and reasoned.