itself. For being you is not being musical; for you are not musical in virtue of yourself. What,
then, you are in virtue of yourself is your essence.
However, it is not clear that the phrase“in virtue of yourself”should be understood
as“in virtue of the fact that you exist.”^47 Moreover, even if David Lewis is an ontic
essence for himself, it is not clear that David Lewis is hisultimateontic essence. I am
inclined to think that, from an Aristotelian perspective, David Lewis’s substantial
form has at least as much right to be consideredanontic essence, and perhaps is the
ultimate essence of David Lewis.^48
A better candidate for a historical proponent of this view is Descartes circaThe
Principles of Philosophy.^49 In this work, Descartes defends the view that each sub-
stance has one principle attribute, which constitutes its“essence.”^50 A given sub-
stance cannot have more than one principle attribute, for if it did, it would have more
than one nature or essence, and this is impossible.^51 For this reason, it is plausible to
attribute to Descartes the view that the principle attribute of a substance is that which
grounds the essence of that substance. For corporeal substances, the principle
attribute is extension, and for incorporeal substances, the principle attribute is
thought.^52 Strictly, each substance has its own numerically distinct principle attri-
bute: there is no common universal that all corporeal substances participate in, for
example.^53 But interestingly, Descartes also suggests that each substance is numer-
ically identical with its principle attribute.^54 It would follow then that each substance
is a ground of its total propositional essence. Descartes rejects substantial forms, and
it is dubious that Descartes took the parts of an extended substance to also be
(^47) Koslicki (2012a: 191) suggests that essentialist truths are grounded in identities of the objects of the
essences, which is in the neighborhood of the view under discussion. 48
Cohen (2009: 204–6) says that definable things, such as universals, are their own essences, but that
Socrates is not his own essence, and that the essence of a thing is its form. Tahko (2013: 55) identifies form
and essence in Aristotle, citingMetaphysicsVII.7, 1032b1–2 (Aristotle 1984b: 1630); we’ll have more to say
about this putative identification soon. But Tahko (2013: 55) also says that essences are primitive for
Aristotle and not grounded in anything else. 49
Descartes is not the only plausible historical candidate. According to Normore (2012: 90, 95),
Ockham identified himself with both his existence and essence. Matsen (1974: 103) claims that Alessandro
Achillini defends the“essential”identity of essence and existence in creatures. See also Gilson (1952: 1012).
Kok (2014: 523–4) argues that Buridan identifies a thing with its essence. Conti (2014b: 559–62) says that
Paul of Venice claims that there is merely a formal difference or difference in reason between a creature and
its essence. Bakker (2014: 607–8) claims that Albert the Great identified a thing with its essence. Galluzzo
(2014: 250) notes that Aquinas appears to identify“separated substances”with their own essences. In this
context, one also must wonder what Locke (1979: 417) meant when he said that essence is the very being of
the thing whereby it is what it is. 50
51 SeePrinciplesI.53 (Descartes 1992: 210).
52 See Descartes (1992: 298).
InThe World, Descartes (1992: 92) asserts that extension is the“true form and essence”of material
bodies; in theDiscourse on the Method, Descartes (1992: 127) asserts that he is a thing whose essence is
thinking. 53
54 See Secada (2000: 205–6) for a discussion of individual essences in Descartes.
SeePrinciplesI.62–3 (Descartes 1992: 214–15). What is suggested is that, in reality, a substance and
its principle attribute are the same.