 Now, given the above interpretation of the said-of and present-in relation, a primary substance is a particular that is non-accidental. It must be admitted that it is difficult to say exactly what it means to say that a particular is non-accidental. In highlighting the fact that primary substances are not the sorts of beings that can be accidents, Aristotle seems to be indicating both that they are not predicated of anything accidentally and that they are not entities that are manifestly temporary, accidentally characterized, or artificially unified, such as Socrates-seated-in-a-chair. Similarly, by treating them as not said-of anything, Aristotle draws attention to the fact that primary substances are not predicated of anything either. Rather, they are themselves essential unities, and indeed not predicable at all. Beyond these few remarks, however, it is difficult to say exactly, given only what is made explicit in the Pre-predicamenta what a primary substance is. But this, one might argue, is appropriate for a metaphysically fundamental entity — we can say of it what it is not, but because it is so basic, we lack the vocabulary to say in an informative way what it is. And indeed, Aristotle thinks that primary substances are fundamental in this way since he thinks that all other entities bear some type of asymmetric dependence relation to primary substances (2a34–2b6).