The Value of Hammers and True Beliefs

September 14, 2008

In each hand, you hold a hammer.  As far as their intrinsic qualities are concerned, the two hammers are indistinguishable.  Hence, they would seem to be equally useful for doing things like pounding in nails, tearing down walls, and “fixing” crashed Macintosh computers.  However, the hammers do differ in one respect: the hammer in your right hand belongs to you, the hammer in your left hand belongs to a neighbor, who has explicitly told you that you may not use his hammer.  Here, then, is a question:

Is the hammer in your right hand more useful (to you) than the hammer in your left hand?

I claim the answer is ‘yes’.  But I do not wish to disagree with you if you say that there is a sense in which they are equally useful.  I only wish to claim that there is a sense in which the hammer in your right hand–the one that you have the right to use–is more useful than the hammer in your left hand.  Let us call the sense of ‘useful’ according to which the hammer in your right is more useful than the hammer in your left ‘instrumental-cum-normative usefulness’.  And, if you believe there is such a thing, we can call the sense of ‘useful’ according to which the two hammers are equally useful ‘pure instrumental usefulness’.

That’s enough about hammers.  What about true beliefs?   Read the rest of this entry »


Time Travelers and Their Temporal Parts

September 12, 2008

In Four-Dimensionalism, Ted Sider gives the following definition of a temporal part (p. 59):

x is an instantaneous temporal part of y at instant t =df (1) x exists at t, but only at, t; (2) x is part of y at t; and (3) x overlaps at t everything that is part of y at t.

I am a little puzzled about how to apply this definition to temporal parts of time travelers. Following Lewis, let’s distinguish external time (physical, objective) and personal time (subjective, “inner”). Intuitively, I think that different instants of personal time correspond to different temporal parts. I will explain why I believe that this intuition is incompatible with Sider’s definition of a temporal part, and it would be great if someone could tell me whether I am right.

Read the rest of this entry »