Note that allowing a murderer to, well, murder, improves his economic welfare - it increases his economic utility. Yet murdering is a net negative in the ethicist's utility function.

Economics makes normative claims because economists typically have some relatively uncontroversial normative assumptions - like maximizing economic welfare is a good thing. This is by and large true, but see my counter example above. Also, economists aren't trying to prove that the values they assume are the correct ones. They are assuming certain ethical values and proposing policies that maximize these values.

The two types of utility functions look very similar - the math is the same, both describe goal seeking behavior, etc., but the difference is the preference sets that each describe. Murder can increase utility in the economist's utility function, but not in the ethicist's (under normal circumstances).

Murder can increase utility in the economist's utility function

That is really immaterial though and computationally moot. Ok so his "utility function" is negative. Is that it, is that the difference? Besides, I would argue that reevaluating it on those terms does a poor job of actually describing motivation in a coherent set.

Yet murdering is a net negative in the ethicist's utility function.

It isn't in the economists? These things aren't neutral.

The broader aspect that economists seek is normative. You said it yourself in the economists a... (read more)

The Difference Between Utility and Utility

by Matt_Simpson 1 min read2nd Dec 200916 comments

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Recently I argued that the economist's utility function and the ethicist's utility function are not the same.  The nutshell argument is that they are created for different purposes - one is an attempt to describe the actions we actually take and the other is an attempt to summarize our true values (i.e., what we should do).  I just ran across a somewhat older post over at Black Belt Bayesian arguing this very point.  Excerpt:

Economics (of the neoclassical kind) models consumers and other economic actors as such utility maximizers... Utility is not something you can experience. It’s just a mathematical construct used to describe the optimization structure in your behavior...

Consequentialist ethics says an act is right if its consequences are good. Moral behavior here amounts to being a utility maximizer. What’s “utility”? It’s whatever a moral agent is supposed to strive toward. Bentham’s original utilitarianism said utility was pleasure minus pain; nowadays any consequentalist theory tends to be called “utilitarian” if it says you should maximize some measure of welfare, summed over all individuals... Take note: not all utility maximizers are utilitarians.

There’s no necessary connection between these two kinds of utility other than that they use the same math. It’s possible to make up a utilitarian theory where ethical utility is the sum of everyone’s economic utility (calibrated somehow), but this is just one of many possibilities. Anyone trying to reason about one kind of utility through the other is on shaky ground.