Dear John, (01)
> MW> This is also what we now do with a 4-dimensionalist
> > approach. However, it is this approach that also demonstrates,
> > as I explained to Duane that employee is not a subtype of
> > person, taking person as the person-for-the-whole-of-their-life.
>
> Subtype has a very clear and simple definition: X < Y
> means that every instance of X is an instance of Y. (02)
MW: I agree of course.
>
> This is true in a 3-D version and in a 4-D version. When a
> person stops being an employee, there is no employee. But
> as long as a person is an employee, that employee is one
> and the same individual as that person. (03)
MW: Under 4 dimensionalism with extensionalism, identity is based
on being the same spatio-temporal extent. So Matthew West the
employee of Shell is only the same thing as Matthew West the person
if Matthew West is an employee of Shell for the whole of his life. (04)
MW: Matthew West the employee is a temporal part of Matthew West
the person, but that does not make them the same thing, it only
means there is a temporal whole-part relationship between them.
>
> MW> Let us look at a couple of possibilities here:
>
> This definition covers every case. It is true in a 3-D
> version and in a 4-D version. It implies that the entire
> spatiotemporal extent of Employee is included in the
> spatiotemporal extent of Person. (05)
MW: No it does not. Being a temporal part of a person implies
this, but subtype/supertype requires that instances of the subtype
are instances of the supertype. The employee instance is not
a person-for-the-whole-of-their-life, so employee is not a subtype
of person. (06)
MW: I accept that under 3 dimensionalism employee is a subtype of
person, because the person is wholly present at each point in time.
You then ahve to temporally index what is going on. In my view a
great strength of 4-dimensioalism is that it requires a stronger
approach to temporality that makes these differences more explicit. (07)
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