This article addresses some crucial assumptions that are rarely acknowledged when organisms and machines are compared. We begin by presenting a short historical reconstruction of the concept of “machine.” We show that there has never been a unique and widely accepted definition of “machine” and that the extant definitions are based on specific technologies. Then we argue that, despite the concept's ambiguity, we can still defend a more robust, specific, and useful notion of machine analogy that accounts for successful strategies (...) in connecting specific devices (or mechanisms) with particular living phenomena. For that purpose, we distinguish between what we call “generic identity” and proper “machine analogy.” We suggest that “generic identity”—which, roughly stated, presumes that some sort of vague similarity might exist between organisms and machines—is a source of the confusion haunting many persistent disagreements and that, accordingly, it should be dismissed. Instead, we endorse a particular form of “machine analogy” where the relation between organic phenomena and mechanical devices is not generic but specific and grounded on the identification of shared “invariants.” We propose that the machine analogy is a kind of analogy as proportion and we elucidate how this is used or might be used in scientific practices. We finally argue that while organisms are not machines in a generic sense, they might share many robust “invariants,” which justify the scientists' use of machine analogies for grasping living phenomena. (shrink)