Vernon Pratt

It has been claimed that in a single line of development the science of taxonomy stretches from Aristotle to the present day and that the Aristotelian 'essence' lies at the heart of much later thought about grouping. I try to establish some basic features of Aristotle's conception of 'essence', and then consider in more detail the conception of essence that entered into 18th century thought about classification, with a view to establishing discontinuities. 18th century thought, I note, has two kinds of essence, real and nominal, and I consider the view that a 'natural' classification in that context should be understood as one which is based on real essences. In place of this thesis, I advocate the view that the hidden foundation of 18th century systematics is a very restrictive articulation of the visual field which gives sense to the possibility of grouping according to the sum total of observable similarities and differences: and that it is this possibility that a 'natural' classification was conceived of as realising

The rationale for the common rejection of classical societal functionalism is that it entails treating a society as an intelligent purposer, capable of directing its own internal organization in furtherance of survival. But a more acceptable alternative account of the origins of a society's functional organization is conceivable: the individual unconsciously recognizes the needs of his group and directs his behaviour so that they are met. The plausibility of this explanation hangs on whether selection between groups occurs to any significant extent, however, and it is therefore on this question that the plausibility of classical societal functionalism itself depends.

For Leibniz, it was a requirement upon the `fundamentally real' to have a `principle of unity'. What does this mean?One general point is that Substance cannot be understood as pure extension. But there is a particular point about cohesion: a real thing had to have some means by which its parts were stuck together. But Leibniz' insistence on `unity' is also an insistence on indivisibility. Under this head there is first the point that there appears to be a contradiction between extension and being incapable of being cut in two. Second, Leibniz uses the notion of `indivisibility' to mark the following distinction among things made up of parts: those which cannot be split without being destroyed; and the rest . To be `indivisible' is to be of the first type. Leibniz' insistence that the truly real must be `indivisible' is then his insistence that the truly real, if it is made up of parts, must be a thing with `integrity', i.e. not an aggregate.What does Leibniz think of as the connection between what is truly real and the possession of `integrity'? He took from Scholasticism the doctrine that action is necessarily attributed to a substance having `integrity', contructing what was in effect a theory of action with two parts: only self-subsistent substances can act; and an action is an origination of change. Leibniz thus insists that self-subsistent substances must be indivisible, in the sense that they cannot be mere aggregates. Aggregates cannot act, and self-subsistence in effect is the capacity for action. This is the most fundamental reason Leibniz had for insisting that the truly real must have a `principle of unity'.It is misleading to speak of Leibniz reintroducing the Scholastic form-and-matter conception of substance for the following reasons: the Scholastic `form' precisely lacked a `principle of action'; and during the period when it is suggested that Leibniz' conception was essentially Scholastic he was defending the view that what his `form' informed was not matter at all but what he called a `metaphysical point'