Metaphysics of natural species (5)

Abstract

The fifth lesson recalled the opposing arguments between Locke and Leibniz. For Locke (the Philalèthe of the New Essays), "the reduction of things into species relates only to the ideas we have of them, which is sufficient to distinguish them by names". For Leibniz, who thinks in the register of the infinite possible, essences are eternal: they exist in the divine understanding, where they represent necessary truths, in other words, accessible from any possible world. Leibniz believes in a logical space of possibilities, dependent on God's free choice of one world rather than another, where individual substances are grouped together according to common properties that harmoniously complement each other, drawing natural boundaries between species. In addition to the modal argument, Leibniz invokes the causal history of species and generation (hence the difference between mathematical and physical species):" Two physical individuals will never be perfectly [of a species, for they will never be perfectly] alike, and, what is more, the same individual will pass from species to species, for it is never similar in everything to itself beyond a moment." It is this grounding in nature that prevents us from granting conceptualism as broad a scope as Locke claims:

"[...] whatever regulations men make for their names and for the rights attached to names, provided their regulations are followed or bound and intelligible, they will be founded in reality, and they will not be able to imagine species that nature, which includes even possibilities, has not made or distinguished before them [....] We can therefore say that everything we distinguish or compare with truth, nature also distinguishes or makes suitable, although she has distinctions and comparisons that we do not know and which may be better than ours. So it will still take a great deal of care and experience to assign genera and species in a way that is close enough to nature."

A VI, 14, G, p. 288

Where Locke suggested that we didn't need to go to India to know that a feline with big orange stripes is a tiger, causal history, for Leibniz is part and parcel of our knowledge of species and real distinctions in nature:

"[...] the deeper we go into the generation of species, and the more we follow in the arrangements the conditions required for them, the closer we will come to the natural order."

A VI, vi, G, p. 310

There are therefore foundations for distinct species in nature, and the further we examine (metaphysically) the possibilities, the better we'll understand what is. There is therefore nothing to prevent us from thinking of "ruptures", nor, contra Locke, a knowledge of the essences of natural species, by which we mean not just simple modes (Locke), but substances (§ 18; G, p. 273). Whereas, for Locke, our classifications (sortal concepts) are the work of the understanding and don't have to correspond to real divisions or joints in the world, for Leibniz, the more empirical evidence we accumulate, the more our terms of natural species will really refer to truly linked groups in the world. No rupture, but harmony between understanding and nature. To Locke's conceptualist, unrealistic and skeptical conception, Leibniz opposes a more optimistic vision, which does not exclude the possibility of knowledge of the internal constitution of things, or even of "fixed traits" constitutive of this or that species (for example, rationality for the human species [VI, § 22, G, p. 293], which forbids the plurality of species within humanity).

We concluded with a discussion of Locke's and Leibniz's respective contributions to our project. For Locke, 1. all our classifications are the product of nominal essences, rendering the real essences of Aristotle useless. Science has no use for essentialism. In the case of substances, the nominal essence is no different from the real essence (the internal constitution of things). We don't know the nature of natural substances and species. 2. On the semantic level: the meaning of natural species terms (or sortal concepts) is determined by the description we make, at the whim of our abstractions, of the sensible properties of individuals. 3. Nature makes no leaps. Individuals differ from each other only by degrees in their internal constitution. 4. All possible natural species are real, have been real or will be real. For Leibniz: 1. there are real divisions in nature, and these form the basis of the divisions we make of the world; 2. these divisions describe a logical space of possibilities in which essences unfold, in full conformity with the divine choice of this world among an infinite number of possible worlds.

For us, the Leibnizian approach has undeniable merits: it provides the conditions for reflection on the possible articulation betweena priori and experience, and on the way in which the idea of necessity could be combined with that of a posteriori knowledge (a point that we shall see is fundamental for Kripke). This can be seen as a gain in relation to Locke, who, in his critique of the Cartesian argument, contests the possibility of knowledge being confined to a priori knowledge, assuming that we have some form of immediate rational intuition of essences. If we take a different view of the possible grasp of essences, as Leibniz does, then the argument put forward by the Lockeans and Humians loses its force. This possible space left to thea priori, combined with a reflection of modalities in an a posteriori framework, opens up interesting epistemological perspectives in our search for definitional criteria for natural species.