The Principle of Parsimony, and the apparently related matter of the supposed inadmissibility of untestable hypotheses, are examined in the light of certain examples taken from the history of science. It is urged that many important new ideas would not have occurred had their authors not disregarded both principles entirely. Illustrations are drawn from the manner in which 18th century biologists dealt with the problem of organizing a rapidly growing body of knowledge, from the history of the type concept in zoology, and from the 18th and 19th century controversies on the history of the earth and on biogeography.