by Garreth Matthews
“[Aristotelian essentialism] is the doctrine that some of the attributes of a thing (quite independently of the language in which the thing is referred to, if at all) may be essential to the thing and others accidental. E.g., a man, or talking animal, or featherless biped (for they are all the same things), is essentially rational and accidentally two-legged and talkative, not merely qua man but qua itself.” ~ W.V. Quine
Quine does not actually say that what he calls “Aristotelian essentialism” is Aristotle’s own doctrine, i.e., that it is Aristotle’s essentialism. Nor does he make any reference, in discussing “Aristotelian essentialism,” either to Aristotle’s own writing or to any commentaries on Aristotle’s writing. On the other hand, he does nothing to warn his readers that the doctrine he is discussing may be only Aristotle-inspired and not the real thing; so I shall take what Quine says as an attempted explication of Aristotle’s own doctrine. Moreover, in this essay I shall myself mean by “Aristotelian essentialism” Aristotle’s own teaching on this subject, whatever it was.
According to anybody’s essentialism, presumably, some of the attributes of a thing are essential to it, others not. To know what so-and-so’s essentialism comes to, we need to know what an essential attribute is, according to so-and-so. In the next sentence after the quotation above, Quine makes clear that, on his understanding of “Aristotelian essentialism,” an essential attribute is a necessary one. If we follow the modern and quite un-Aristotelian practice of using “property” in place of Quine’s (historically preferable) expression, “attribute,” then we come up with this definition of “essential property”:
p is an essential property of x=df regardless of how x is specified (if at all), x necessarily has p.
According to Ruth Marcus , “Aristotelian essentialism takes it that, is anything is a man or a mammal, it is so necessarily.”(190) Her discussion suggests this definition:
p is an essential property of x=df. p is an essential, property of x and anything that has p has p necessarily.
M.J. Cresswell  says about a related notion, “a per se property,” that if it were not the case that a property could not be per se of one individual and per accidens of another, “few interesting properties could ever hold per se of their subjects.” (93) The implication of Cresswell’s discussion is that Aristotelian essential properties are essential, but not essential properties, whereas according to Marcus’s characterization of Aristotelian essentialism, all essential properties are essential. At stake here might be whether, for example, being red-eyed could be an essential property of a bird of a certain kind (a black-capped vireo, say) though only an accidental property of, for example, human beings.