Book Z of the Metaphysics of Aristotle focuses on the idea of the subject, which is one of the senses in which the term “substance” is used. Z is an important book, because it establishes how substance relates to change and matter. One school of interpretation of Z considers one sense of form to be prior to and more important than matter, and has proposed a different reading of the book. I will call this the “formalistic” approach to substance. Supporters of this school hold that the form comprises itself as a whole individual which may be considered as independent of matter. This school focuses especially on Z 3, 1029a-b, where Aristotle seems to challenge the status of matter as an essential part of substance. This paper deals with two formalist approaches, and stresses some difficulties in understanding Z when following the ideas of D. W. Ross.