In Chapter 1, “Leibniz and the problem of individuation: the historical and philosophical context,” of their book, Substance and Individuation in Leibniz, J.A. Cover and John O’Leary-Hawthorne provide a historical introduction to Leibniz’s views on individuation. In §1, the authors begin by working out the various questions that can be asked within the topic of individuation, particularly as this topic was handed down to Leibniz by scholastic philosophy. They begin by giving their readers a broad overview of the topic, laying out two general approaches that one can take to individuation. In §1.1, they present what they call the blueprint approach.
The blueprint approach seeks to account for an individual by offering a kind of blueprint that will describe what is required in order to bring about that individual. The blueprint is like a recipe, which tells us both the ingredients, the amounts, and their mode of combination. Just like a recipe, “the blueprint for an individual substance would providean account of the constituents of a thing, together with an account of the modes of unification whereby those constituents make up the thing or ontological kind in which one is interested” (11).
For a scholastic trying to offer such a blueprint approach, they would undoubtedly begin with Aristotle and three of his most important notions on this topic: form, matter, and accident. In broad strokes, form was the “unifying principle in matter that yields the sort of unity in which accidents can inhere” (12). Scholastics generally considered accidents to be ontologically dependent upon substances, but not vice versa. The authors thus not that that leaves matter and form to be the basic working concepts with which the blueprint approach will use.
The authors then go on to listing three further constraints that any scholastic would confront with regard to the topic of individuation. The first concerns one’s commitment to other metaphysical facts about substance. They list: (i) the need to distinguish between the matter of a substance and the substance itself, in order to account for the difference between substantial change (generation, annihilation) and mere alteration; (ii) the need to distinguish between a substance’s accidents and its other constituent properties in order to make room for identity through alteration; and (iii) the need to distinguish between a thing’s essence and its existence in order to be able to distinguish between a merely potential being and an actual being.
The second constraint placed upon the blueprint approach regards the intensional commitments that one might have to the very idea of individuality. Here, they list five popular concepts from the scholastics: (i) impredicability; (ii) incommunicability; (iii) identity; (iv) division; and (v) difference or distinction. (I would like to point out that seem to be following J. Gracia in this listing. I will be posting on Gracia’s treatment of the intensionality of individuality in the near future).
The third constraint they identify as the paradigm case that one takes to be a substance. This is the extensional aspect of the problem. For the scholastics, there was not only a division between substance and accident, but a hierarchy between substances “that exist at the metaphysical groundfloor” and merely enduring things that are “metaphysically second rate.” This finds its expression in the scholastic distinction between substances per se and substances per accidens (something like mere aggregates). This requires that scholastics would be trying to account for the real unity in substances per se that second-rate heaps lack. Furthermore, scholastics were also constrained by their theology as well. For them, substances could be spiritual beings (such as angels).
The authors next explain that there are three different levels of generality at play in the blueprint approach to individuation that correspond with three different questions. First, one can try to offer a schematic blueprint for substance qua substance; that is, one that abstracts away from any given particular substance and any particular kind of substance. This approach corresponds with the question, “What is it for a thing to be an individual substance?” (15). Second, one can begin by trying to build a “portfolio of blueprints,” which is to say to show a blueprint that abstracts away from the features of any particular kind of substance and offers a schematic for each of the fundamental different kinds of substances (spiritual substance, physical substance, etc.). This approach corresponds with the question “What is it for a thing to be the kind of substance that it is?” The third approach is to try to offer a blueprint for particular individuals–not for what makes Socrates Socrates, but what makes any individual x the very individual that it is. This approach corresponds with the question, “What is it for a thing to be the very individual substance that it is?”
The authors note that these three different levels of generality raise the problem of the methodological starting point for the problem of individuation. One could begin at the highest level of abstraction and proceed downwards through filling in detail through differentia; or, alternatively, one could begin at the lowest level and proceed upwards by abstraction. In the latter case, one begins at the level of kind, fills in differentia for the different kinds, then proceeds by way of abstraction to what is common between the different kinds to the highest level of generality. They warn that because of the wideness of application of the concept of substance, it may be impossible to reach a coherent view at this highest level–consider how it might be impossible to find common features between the individuations of spiritual and physical substances.
The authors then proceed to §1.2, in which they describe an alternative approach, called the modal approach, to individuation. See next post here.
 Cover, J.A.; John O’Leary-Hawthorne, Substance and Individuation in Leibniz, (New York: Cambridge University Press, 1999).