It seems to be a wide-spread view in Aristotle scholarship, almost a dogma, that matter does not qualify as being separate. I do not mean here being separate in account, but another sense of separation characteristic for being a substance in a sense that I will call here ‘separation in substrate’. That there is a distinction in Aristotle between at least two senses of being separate characteristic for certain types of substance is clearly indicated e.g. in Metaphysics H.1 1042a25-32. There substantial forms are characterised as being separate in account, while compound substances are characterised as being ‘separate simpliciter’. By being separate in substrate I mean something comprised by being separate simpliciter, namely not to ‘inhere’ in any substrate, or equivalently, to be an ultimate subject of predication. Advocates of the ‘orthodox view’ that matter is not separate – not separate simpliciter and thus not separate in substrate - include for instance Ross (1924), Frede & Patzig (1988), Morrison (1985), Dufour (1999) and Corkum (2013). I will argue here that the orthodox view is mistaken.
Many arguments for the orthodox view seem naturally to be based on the respective interpretation of what separation of substance - i.e. simpliciter - means. This, however, is unfortunately a matter of substantial controversy. Among the many suggested interpretations separation (simpliciter) is equated with existential independence (Fine 1984), with essential independence (Peramatzis 2011), with (numerical) distinctness (Morrison 1985) or with spatial separation (Dufour 1999). I disagree with all these interpretations. I cannot, however, engage here in a discussion about the right interpretation and argue duly for my own. I will therefore limit myself to a discussion where an engagement in this controversy seems not required.
I will, first, address two arguments, one by Morrison (1985) and one by Dufour (1999), for the orthodox view. Both base their arguments on passages in Aristotle’s physical writings (Physics, On Generation and Corruption). Both ignore, however, the difference of the contexts in which Aristotle speaks about separation in these passages and in passages about separation of substance. As a consequence, Morrison and Dufour conflate the different senses of ‘being separate’ involved in these passages. This conflation, which also seems to entail an inconsistency in Aristotle, thus seems to render the two arguments unsound.
I will further argue against an apparently quite common interpretation of a prominent passage about matter and separation in Metaphysics Z.3 1029a27-31 (an exception here is Marc 2012). This common interpretation directly supports the orthodox view. This interpretation, however, is, as I will argue, not the only possible one. And it seems to entail in addition that matter is not substance (in any sense). It therefore seems to be at odds with other passages in Aristotle, where the status of being a substance seems clearly attributed to matter. This common interpretation should thus be rejected in favour of an alternative one that allows for or even suggests that matter is separate, i.e. separate in substrate.