Aristotle's notion of matter has been seen either as unintelligible, it being some mysterious potential entity that is nothing in its own right, or as simply the notion of an everyday object. The latter is the common assumption in contemporary approaches to hylomorphism, but as has been pointed out, especially by scholars with a background in ancient philosophy, if we conceive of matter as an object itself we cannot account for the unity of hylomorphic substances. Thus, they assume that a (...) hylomorphic substance is an essential unity and matter not a constituent at all. This solution to the problem of unity, however, brings us back to the mysterious notion of matter. For these reasons, I will revisit Aristotle's conception of matter in this paper. I will argue that an understanding of form as a cause of being requires that matter be an independent constituent of the individual substance. However, I agree that the conception of matter as an individual object with an essence makes it impossible to solve the problem of unity. We therefore need to take seriously Aristotle's assertion that matter is nothing in its own right and not an individual. By denying that matter is an individual, Aristotle does not introduce a mysterious entity, nor does he deny that it can be identified independently of the whole; instead, matter for Aristotle is an irreducible plurality, and this explains why it is not an individual and has no essence. I will conclude with some observations on how this gives rise to two competing versions of hylomorphic constitution. (shrink)