I reply only to David's comments to me, editing the email so as to
reduce the length of the message.  I leave others to take up other
points.

You exclude certain practices from science because they are too vague.
I do not see the basis for this. By the standards of space-telescopes,
the measurements of, say Copernicus or Tycho may have been imprecise,
but does that make them any less scientists? No. You say inflation is
imprecise. But (a) I could say "The government sets its goal as n%
inflation measured by the all items retail price index ... as precise
as you care to make it. (b) There is imprecision and "negotiation" in
science, as much of the sociology of scientific knowledge literature
makes clear. By requiring that science involve the application of
tried and tested theories you are confining science to what might be
called Kuhnian normal science.

In our culture, to call something science is, whether we like it or
not, to express approval, and to say that something is not science is
to denigrate it (I should perhaps add some qualifications about what
the science is being used for, but the point would still stand). Maybe
it should not be like that, but that is the way things are. Thus by
privileging anything that is not precise the effect is to reinforce
the profession's fondness for abstract theory (mathematics is the only
thing that can be completely precise) and, in practice, even if this
is not intended, to denigrate the messier practices of much that
should, in my view, be considered real science because it is trying to
understand what is going on in the world. The goal may be precision
(no quarrel with that) but that is a different issue. Surely
scientists who tackle important problems are scientists as much as
those who leave aside difficult and important problems for easier ones
that they can tackle more rigorously.

That is why I think the science/art of economics distinction is
dangerous (at least today - in other contexts the implications might
be different).

To me, the issues of whether something is science and whether it is
successful science are different. By defining science as being precise
and relying on well-tested theories, you are conflating the two.

Roger

> Roger asks me whether two statements that "concern how the world is, yet they have obvious implications for policy are art or science. I reprint one in the interest of space.
>
> The government has decided that it wishes to reduce inflation by a
> specific amount, and that it wants to achieve this through policies
> that do not interfere with certain other objectives. The economist
> writes a report in which he or she shows that adopting a certain list
> of policies will achieve that objective. Does it make any difference
> whether the list of "other objectives" is comprehensive and clearly
> specified or vague and even non-existent?
>
> This is definitely art in my view. It is the engineering branch of art. No one says that art cannot, and should not be objective.  Why is this question not in science?  Because the issues are too vague--definitions of inflation involve many complications, and the policies that he or she will discuss will have implications that go way beyond economic science.  Ditto for his other example.
>
> So in answer to his question:
>
> Is the difference that if the economist judges policy according to the
> government's stated objectives, the economist is engaging in science;
> but if the economist judges policy according to objectives that are
> not explicitly stated, the economist is combining scientific knowledge
> with judgments about the criteria that should be used to evaluate
> policy, and is therefore engaging in art?
>
> My answer is no--that is not the defining aspect. The defining aspect is whether the questions are formulated in a clear enough manner so that one can provide an answer based on a tested economic theory that does not raise other issues that would need to be answered if one is to act on the advice.  In my view most of what economists do is not science. It is a type of engineering/art.
>
> Don't get me wrong. The definition of science is not the point. The appropriate methodology is the point. The distinction doesn't matter except in terms of the methodology used. As J.N. Keynes said, the methodology for the policy art of economics is much broader than the methodology for the science of economics. The reason I think the distinction is worth raising is that to use the methodology of science to answer a question in the art of economics means that one is limiting one's consideration of issues and missing many connections, and is not doing a good job of policy advice. To do good policy advice you have to take in all relevant dimensions of the problem, or at least be aware of them and point them out. Most of our economic models don't do that, and thus leave policy issues unaddressed.
>
> This policy art can be highly technical, and or it can be looser--the nature of the art depends on the nature of the question being asked. So I am arguing for using science in economics in a highly restrictive way--to refer to pure science. I recognize that this is only a definition--we could distinguish realistic science and pure science as Pigou did, and say that what I am calling engineering/art is actually realistic science. That would be fine with me as long as (1) one did not claim that policy recommendations that follow from it had the backing of pure economic science, but were based on art, and (2) one allowed broad methodological discussions of the policy, and did not try to shut up critics with the argument that they are not doing science.