  Aristotle rejects this approach for several reasons, including most notably that he thinks that certain non-essential features satisfy the definition. Thus, beyond the categorical and logical features (everyone is such as to be either identical or not identical with the number nine), Aristotle recognizes a category of properties which he calls idia (Cat. 3a21, 4a10; Top. 102a18–30, 134a5–135b6), now usually known by their Medieval Latin rendering propria. Propria are non-essential properties which flow from the essence of a kind, such that they are necessary to that kind even without being essential. For instance, if we suppose that being rational is essential to human beings, then it will follow that every human being is capable of grammar.  Being capable of grammar is not the same property as being rational, though it follows from it. Aristotle assumes his readers will appreciate that being rational asymmetrically explains being capable of grammar, even though, necessarily, something is rational if and only if it is also capable of grammar. Thus, because it is explanatorily prior, being rational has a better claim to being the essence of human beings than does being capable of grammar.   Consequently, Aristotle’s essentialism is more fine-grained than mere modal essentialism.  Aristotelian essentialism holds: