Albertus magnus and the error of Ptolemy: Metaphysics and the origins of empirical research programs

Is our science of the physical world a matter of theoretical description with predictive value, or is it instead a search for the productive causes of observed phenomena? Ancient astronomers such as Ptolemy maintained the former; ancient cosmologists such as Aristotle the latter. This debate is a central theme in Albert Magnus's thirteenth-century Aristotelian commentaries. This paper shows how Albert defended the possibility of empirical science aimed at demonstrating the causes of observed phenomena. In the course of his defense, Albert identifies a specific error committed by Ptolemy concerning the subject of physical theory. The identification and correction of this error provides the basis upon which a proper metaphysical foundation for the empirical sciences can be laid. This foundation is nothing other than the recovery of the Aristotelian notion of form as the immanent intelligibility of physical natures.