Wednesday, April 1, 2015

Weak and strong incommensurability

X and Y are weakly incommensurable iff there is a dimension of evaluation where X beats Y and a dimension of evaluation where Y beats X. X and Y are strongly incommensurable iff they are weakly incommensurable and a rational agent doesn't have on balance reason to choose X over Y and doesn't have on balance reason to choose Y over X.

Weak incommensurability is precisely what is needed for the possibility of a rational agent choosing either over the other.

Weak incommensurability is evidence of strong incommensurability. But there are cases where weak incommensurability fails to yield strong incommensurability. One kind of case is extremity. If one is choosing between being a superb nurse and a very mediocre mathematician, there is weak incommensurability, but one may have on balance reason to be a nurse (all other things being equal). But when choosing between being a nurse and a mathematician and one's professional quality would be moderately close, it's also strongly incommensurable.


Heath White said...

Weak incommensurability seems pretty weak to me, too weak to make sense of a rational agent choosing either way.

For example, suppose I am deciding whether to buy one of two used cars. One is perfect except it has a small ding in the driver's door. The other is a disaster: flat tires, leaking oil, half-collapsed roof, no rear window, peeling paint on the hood ... but a pristine driver's side door.

It's not all that hard to choose, is it?

Alexander R Pruss said...

This points to the important point that all this depends on how finely grained the dimensions are. For instance if the dimension is "aesthetically relevant damage", maybe we do have domination.
But I like to fine grain this, to explain how an agent can in fact make the stupid choice.