The Development of the Philosophy of Species 309
PHILOSOPHICAL TERMINOLOGY
Epistemology: The study of the conditions under which knowledge is gained
and justified. Adj. epistemic.
Ontology: The study of the metaphysical kinds of objects that exist, such as
number, sets, classes, or relations. Adj. ontic.
Metaphysics: The study of the fundamental nature of reality and being. This is
typically focused upon issues that cannot be resolved through science,
and includes concepts like universals, individuals, substance, space,
time, mind, reality, and so on. ONTOLOGY is a part of metaphysics.
Essence: Either what makes something what it is (the constitutive version), or
something that is necessary for the thing to be what it is (the modal
version). A fixed nature. One or all of the necessary properties of a
class of things. In older (scholastic) writings, the essence is the form of
objects, independently of their substance.
Essentialism: The view that some objects have essential properties. Usually,
the view that classes of things are defined by their essential properties,
or essences. Sometimes expressed modally as the [jointly] necessary
and [severally] sufficient properties (JNSSPs) of a class; which is to say
these properties must be properties of all members of the class (neces-
sity) and all of them jointly are enough to specify the class.
Class: A set of things that fall under the defining concept of the class. The
extension of a set’s INTENSION. Alternative definition: that which is clas-
sified, a taxon.
Set: A collection of things or ideas, however formed. Sets with definitions are
intensional sets.
Intension/Extension: The intension (not to be confused with intention) is the
meaning or connotation of an expression. The extension is the state
of affairs, or objects, that fall under the intension of an expression,
or denotation. Roughly, intension marks out the defining properties,
while extension marks out the things that are defined.
Monothetic/Polythetic: Monothetic groups are classified by sharing a single
set of properties, the absence of any one of which excludes an
individual from the group. In systematics, a monothetic species is a
monotypic species. In philosophy, a monothetic group is generally
called a CLASS. A polythetic group is one formed from a majority or
threshold value of shared properties, and maps in systematics to a
polytypic group or taxon. In philosophy, Wittgensteinian classification
by similarities are often called polythetic classes.
Names and Nomenclature
Nomenclature is a major facet of the species problem, but it is a problem of opera-
tional convenience. Although Linnaeus thought that once identified, binomials
would be stable, it turns out that neither genus nor species names are in fact stable.
In one group I examined—pinnipeds—as many as 75% of species names have been