Chierchia models a kind as an individual concept: at each situation it picks out the sum of its
instances, and it has no value where it has none. The operator 'down', ∩, takes a property to the
concept of the largest member of its extension at each situation, which is the property's kind
where that concept is a kind, and the operator 'up', ∪, takes a kind to the property of being one
of its instances, the parts of its value. ∩ is ι applied at each situation, and ∪ its partial
inverse, Set.Iic.
∩ undoes ∪, and ∪ undoes ∩ on a property closed downward
wherever ∩ is defined, that is, wherever the property has instances its extension has a largest
member. Closure under sums gives the largest member, not closure downward: over a complete
semilattice ∩ is defined on a property closed under arbitrary sums, so ∪ undoes ∩ on one that is
also closed downward (Kind.up_down_of_sSup_mem), and ∩ is defined on a finite property closed
under binary sums (Kind.down_isSome_of_supClosed). On the plural of a singular property, ∪∩
restores the atoms beneath the pluralities. ∩ is
undefined for a singular property when no kind is singular wherever
it has a value. Derived kind predication, which applies a predicate of objects to a kind by
quantifying existentially over its instances, is Quantifier.Det.some (Kind.up k s).
Main definitions
Kind.up: ∪, the instances of a kind at a situation.Kind.down: ∩, the concept of the largest member of a property's extension.
Implementation notes
The set of kinds is a parameter K : Set (S → Option E) of the theorems that need it, primitive
as in Chierchia. Chierchia states (17c) with AT_P "the set that generates P under PL", which is
read here as the atoms beneath members of P. Read as the singular property whose plural P
is, (17c) fails at a situation with exactly one instance, where the plural has no member and ∩
no value (Studies/Chierchia1998.lean).
References