Species

102 Species

between formal and material significata, so that he could be a “predicate essentia-
list” and yet a nominalist.^242 This distinction has long standing.
A possible source of the notion that biological species before Darwin were seen
to be essentialist may be John Dewey’s famous essay of 1909 on “The Inuence
of Darwin on Philosophy.”^243 Here, Dewey presents a nalistic account of Greek
conception of eidos (anachronistically stating that the scholastics translated this as
species, not the Latins). He says that eidos keeps the ux stable, makes individu-
als isolated in space and time keep to a “uniform type of structure and function,”
and that the conception of species as a “xed form and nal cause” was the central
principle of knowledge and nature.^244 But it is xism and nalism that he opposes
to Darwin’s theory, not essentialism. His only mention of essence is a sneering ref-
erence to “the logic that explained that the extinction of re by water through the
formal essence of aqueousness”^245 ; presumably the fault is the use of a formal notion
where an efcient cause is required.
Traditional essentialisms are generally nominal. From Aristotle through to the end
of our period, when people discuss the essences, they are very often discussing what
description or denition is essential for a universal name or term. Locke’s rejection of
Real Essences is a rejection not of the essences of terms, but of things. He rejects mate-
rial essentialism. And it is the material essentialism of biology that is problematic—
did it, as a historical fact, occur before Darwin? And is it required for taxonomy? We
shall see that neither are necessarily the case, although it is likely that the issues were
not so marked as I have expressed them here, and while naturalists do in fact slide from
nominal to material essentialisms from time to time, it is not the identifying truth of
the period that the Received View/Synthetic Historiography asserts.

Essentialism and Natural Systems

Essentialism and typology are two attributes of “traditional” taxonomy that are often
conated (e.g., by Mayr). But they actually represent two distinct aspects of the old
taxonomic categories. Essences are denable, and can be known by rening deni-
tions, and are common to all members of a kind. No member of the kind can not have
an essential property fully and constantly. Types, on the other hand, although the
term is used in various ways throughout the modern period, are somewhat different.
In biological thought, the type of a kind such as a genus can be instantiated more or
less, and can be varied from. They can be abstract—not actually instantiated in any
actual member of the kind, but every member of a kind must exhibit essences. Types
are formal notions, essences are denitional, and while some types may be essential
and some essences may be typical, the two concepts are not identical. Even worse,
there are several types of types. Stevens cites Paul Farber’s taxonomy of types.
According to Farber^246 and Stevens, there are three kinds: collection, classification,
and morphological types:

(^242) Klima 2005.
(^243) Reprinted in Dewey 1997.
(^244) Dewey 1997, 5–6.
(^245) Dewey 1997, 14.
(^246) Farber 1976.