Milton Friedman and many others have expressed the belief that if all the facts are known, the economist's recommendation (for particular policy or other course of action) is beyond dispute by other economists. I believe Friedman made this statement in a footnote in his highly influential essay on Positive Economics from 1953, and I know he has made similar statements on other occasions. It expresses the Popperian view that empirical observation has the power to reject any scientific theory and Friedman also used this idea to criticize, for instance, the Austrian fixation (most prominently defended by Ludwig von Mises) that economics is an à priori science and that economic facts are reachable only through logic and not through observation.
If neither Austrian (or other disbeliever in the power of observation) party to an intellectual dispute abandons his logic in favour of that of the other fellow, Friedman says that they can only fight (he used this word a number of times). By contrast, if people who believe in the power of observation argue with one another, one can say to the other: "tell me which phenomena you expect not to observe if you are right and I will do likewise". Certainly the latter scenario is more appealing.
I am a great fan of Milton Friedman and he is one of my very favourite economists ever. On this issue, I am sceptical that he was right, however. Now I do not believe he actually meant a proper fight (as in fist fight or other nasty business) in case of disagreement. That belief would have been absurd, since metaphysical questions are not resolved by observation and philosophers engaged in metaphysics do not - to the best of my knowledge - normally engage in fights. Rather, what Friedman must have meant was a "fight" as in an unproductive dispute in which one cannot really gain any ground.
But I do not believe this is really true. Take the issue of free will, for instance. This is a metaphysical issue and believers such as myself can only offer very far-fetched scenarios in which empirical observation would inform the issue, but thinking about it can advance the argument and has done so in the past. I believe it was C. S. Lewis who made the argument that determinism (lack of free will) implies skepticism (and must therefore be false), since if I have no free will, any views I hold are mere products of chemicals interacting in my brain, which epistemically offer no support for my belief in anything. Certainly the case for free will would be weaker today were it not from this contribution, due entirely to logic.
Now Milton Friedman would have been right to argue that this has not settled the argument on free will, but I think it is fair to say that the fact that we can at least advance the debate through means of pure logic does indicate that empirical observation is not absolutely required, though it does of course help a great deal. One could also, of course, ask what empirical evidence there is to support the view that theories falsifiable on grounds of observation are better than are theories which are not falsifiable on empirical grounds. In other words, what observation would reject the idea that observation is epistemically sound basis for rejecting ideas?
The idea that there are moral facts is another reason to be sceptical of the idea that disagreements vanish as empirical facts become known. For instance, if it were made quite clear that immigration restrictions are absolutely required to maximize (let's say global) welfare, I still would not be a fan of them because I believe they infringe upon moral rights. Alternatively, if it were made quite clear to me that I should sentence an innocent Negro to death because otherwise the bigoted people of some town will rebel and cause death and destruction, I still would not kill the Negro. I take moral rights seriously because I believe there are moral facts, of which moral rights form an integral part. Can I prove this? No, but I can offer reasons to think that there are moral facts out there which depend on things other than well-being. If moral facts are facts of the same epistemic status as empirical facts, then maybe they ought to take precedence as guides for action?
I don't want to sound like I reject the power of observation. I absolutely do not. My point in this blog post is merely to defend facts not readily observed empirically, and to highlight the possibility of using logic to advance one's understanding of them.