Chapter 5 argues that the identification of the form in the mind of the artisan with art amounts to ascribing it the role of efficient cause. As the chapter explains, the form in the mind of the artisan is responsible for both qualified and unqualified coming-to-be. Art is the only form that is an efficient cause, in contrast to the form inherent in the artefact. By resorting to Aristotle’s biological works, the chapter clarifies how artefacts come to lack an inner principle of their behaviour and how this is connected with their lack of an inner principle of unqualified coming-to-be. Two theses in particular are challenged. The first is that the form is transmitted from the mind to the object and, as a result, the form of an artefact is potential, because this is the status of the form in the mind in the artisan. The second thesis is that artefacts are not substances because their forms are not principles of changes. The chapter concludes with a reflection on the relation between eternity and substantiality.