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Mental causes are threatened from two directions: from below, since they would appear to be screened off by lower-order, e.g., neural states; and from within, since they would also appear to be screened off by intrinsic, e.g., syntactical states. A principle needed to parry the first threat -causes should be proportional to their effects- appears to leave us open to the second; for why should unneeded extrinsic detail be any less offensive to proportionality than excess microstructure? I say that the second threat relies on a perversion of proportionality that would lay waste to all causal relations.

Essentialists hold that certain of a thing's properties are specially fundamental, antiessentialists that all of a thing's properties are on a par. As a result, essentialists can explain how, e.g., a statue and its clay are different, but not how they are the same, whereas antiessentialists can explain how they're the same but not how they're different. Ordinarily, though, we reckon them in one sense the same and in another different. ;To accomodate the ordinary view, essentialism and antiessentialism must be brought together. To this end, I identify a property as categorical if its possession in a world speaks to what goes on in that world alone; count essentialist particulars contingently identical in a world if they share their categorical properties there; and introduce antiessentialist, or concrete, particulars as entities for which contingent identity is all the identity there is. Concrete particulars emerge as limiting cases of the essentialist particulars with which they were formerly contrasted, and essentialism and antiessentialism are to that extent reconciled. ;With matters so complicated clarity is at a premium, so the scheme is formalized. Each Kripke model of quantified modal logic is supplemented with a set of properties, constrained so that essences drawn from the set specify what a thing must be like to be the thing it is. When one thing's essence includes another's, they are variants. Properties insensitive to the difference between variants are categorical, and contingent identity is sameness of categorical properties. If concrete things are things existing in one world only, then all their properties are on a par, and they're contingently identical iff properly identical. To show the tractability of reasoning about particulars thus understood, I give a sound and complete logic. ;Formalism isn't an end in itself, but the present formalism pays its way by bringing new clarity to traditional issues: I prove that indiscernibles are identical; give an analysis of kind properties; establish the relativity of cross-world identity between concrete things to kinds; forge new links between modality, time, and potentiality; and give an improved counterfactual account of causation