Against manifestationalism

I recently read Asay and Bordner's (A&B) interesting paper "A modest defense of manifestationalism". Last week I discussed a stricter form of constructive empiricism which holds that we should believe that our best theories correctly describe not observable phenomena but only observed phenomena. A&B explore the same view under the name "manifestationalism". More precisely, they given the following taxonomy:

Scientific realism (SR): Science aims to give us theories that are literally true; acceptance of a theory involves the belief that it is literally true.

Constructive empiricism (CE): Science aims to give us theories that are empirically adequate; acceptance of a theory involves only the belief that it is empirically adequate.

Manifestationalism (M): Science aims to give us theories that are comprehensively manifestly adequate; acceptance of a theory involves only the belief that it is comprehensively manifestly adequate. (A theory is manifestly adequate just in case it correctly describes all observed phenomena.)

I have already mentioned that I don't think it's particularly helpful to frame the realism debate in terms of the aim of science. The interesting position is that of the manifestationalist who believes that scientific theories correctly describe only observed phenomena, and who is agnostic about the unobservable and the observabled-but-unobserved.

A&B clarify that manifest adequacy is not simply truth to the phenomena observed so far, but truth to all phenomena that have ever been or will ever be observed, including those observations that take place outside a scientific context (this is what they mean by comprehensive manifest adequacy). This clarification is important. Belief in nothing more than what has been observed so far entails radical scepticism about the future, a position which is not just implausible but probably psychologically impossible to adopt. M avoids this radical scepticism. M endorses the belief, for example, that I will continue observing my computer screen for as long as I sit here typing; that when I go downstairs to get some food I will observe some bananas in the fruit bowl; etc.

The case for manifestationalism

A&B do not attempt to present a conclusive case for M. They merely try to show that it is not absurd or irrational, but a serious contender in the philosophy of science. I will argue that they fail. Much of A&B's paper is devoted to answering a criticism of M based on the aim of science, which I discussed briefly in my previous post; I will focus on their arguments for M, of which there are three:

1. One possible argument for M appeals to van Fraassen's "vulnerability criterion" of belief, expressed in this passage:

If I believe the theory to be true and not just empirically adequate, my risk of being shown wrong is exactly the risk that the weaker, entailed belief will conflict with actual experience. Meanwhile, by avowing the stronger belief, I place myself in the position of being able to answer more questions, of having a richer, fuller picture of the world, a wealth of opinion so to say, that I can dole out to those who wonder. But, since the extra opinion is not additionally vulnerable, the risk is — in human terms — illusory, and therefore so is the wealth. ... What can I do except express disdain for this appearance of greater courage in embracing additional beliefs which will ex hypothesi never brave a more serious test?

Given two theories that are equally vulnerable, we should believe the logically weaker theory. Van Fraassen uses this to argue for CE, but A&B claim that this argument is really an argument for M, not for CE. We will only ever be able to test our theories against those phenomena that are actually observed; we will never obtain any evidence that could decide between two rival manifestly adequate theories. If I believe a theory to be empirically adequate and not just manifestly adequate, my risk of being shown wrong is exactly the risk that the weaker, entailed belief will conflict with actual experience... M and CE are equally vulnerable and M is logically weaker than CE. So we should accept M.

Of course, the force of this argument for M depends on whether we accept van Fraassen's vulnerability criterion of belief. I won't discuss the case for or against this here. Another question is, are CE and M equally vulnerable? Once the end of science occurs, and all the observations we will ever make have been made, the answer is clearly "yes". However the situation is somewhat trickier from our current position. We can see the problem clearly by asking, exactly which aspects of our best theories should we believe? It's easy for the constructive empiricist to answer this. CE tells us to believe what our theories tell us about the observable world. But M tells us to believe what our theories tell us about the observed world - observed in the past, the present, and the future.

The obvious difficulty here is that we don't know what observations will be made in the future. Consider the following case. My friend Frank has an apparently normal chicken egg. Nobody has ever observed the interior of this egg. Frank decides to put the egg in a box and throw it into a volcano, so that nobody will ever observe its interior (suppose this is part of some bizarre religious ritual). Well, if I accept M, then I must be agnostic about what it in the interior of the egg. Its interior will, in all likelihood, never be observed. But then suppose that while carrying the egg to the volcano, Frank drops it and it breaks, revealing the yolk and egg white.

The point, in the context of the "vulnerability criterion" argument for M, is that since we don't know what will be observed in the future, it's not at all clear that, at the present time, CE and M are equally vulnerable. The manifestationalist believes only that theories are true for what will be observed - if we don't know whether X will be observed, or we have good reason to believe that X won't be observed, then we must be agnostic about X. For this reason the manifestionalist, but not the constructive empiricist, must be agnostic about many things that will ultimately end up being observed. CE is therefore riskier than M, and this pushes us towards CE.

2. A&B suggest that M better captures the spirit of empiricism, which counsels us to limit belief to what in principle to tested against experience. The observations that we can make are constrained by our spatiotemporal location. CE involves belief in entities and processes billions of light-years distant or billions of years in the past, that we could not possibly observe. M offers a more modest position based on the specific position of humans in the universe and the epistemic limits entailed by this.

With this argument, I think that A&B have identified a genuine problem with van Fraassen's formulation of CE, but other versions of CE are less vulnerable to their criticism. We simply need to reconceive what is meant by "observable". I offer one suggestion in this post. The constructive empiricist hold the observable is what could in practice be detected by the unaided senses, given the technology of the time; and no feasible technology currently available would allow us to travel to distant quasars. This conception of observable is of course not precise - there is no absolutely clear line between the observable and unobservable - but this is equally true of van Fraassen's way of drawing the distinction.

3. Finally, A&B argue that the aim of an enterprise should be related to "what an ideal community of practitioners of that enterprise would accomplish under ideal circumstances." The aim of an enterprise should be attainable at least in ideal circumstances. A&B then suggest that the ideal scientific community is a community of people just like us, with the same sensory capacities and occupying the same spatiotemporal location in the universe, but who are devoted exclusively to the development of science. They meticulously and flawless record every observation. They generate theories that perfectly fit the observations. What will the final product of this community be? They will have a theories that are manifestly adequate - but not necessarily true or even empirically adequate. Rival empirically adequate theories will fit the data equally well. Even in ideal circumstances, there is no guarantee that we would produce empirically adequate theories, but we would produce manifestly adequate theories. This favours M.

I have two objections to this argument. First, why should the aim of an enterprise be decided by what an ideal community would achieve? Consider games with impossible aims. The aim of Klondike solitaire is to move all cards to their foundation piles; however, this is not possible even in principle for about 20% of deals. An ideal community of Klondike solitaire players could not move all the cards to their foundation piles in those deals - nevertheless, the aim remains the same.

Second, why suppose that there is a definable "ideal community" of scientists? A&B suppose that the ideal community is limited to our place in space and time; but why? Surely an even better scientific community would be one that existed as soon as complex life was possible, and had been meticulously collecting observations ever since. Would all members of the ideal community have perfectly functioning sensory capacities, e.g. 20/20 vision? Perhaps they would have superhuman capacities, 20/10 or even 20/1 vision perhaps. It isn't at all clear what counts as ideal in this respect.

It's clear that the ideal community will need some superhuman capacities. A&B suggest that ideal community would devote all their time to science, and they record every observation they make. Neither of these things is possible for humans. We need to devote time to other enterprises such as eating food, and we wouldn't be able to record every observation even if we tried. There are simply too many observations, and in any case, a person could not record observations while at the same time generating theories to account for those observations.

The problem for A&B is that in order to ensure that the ideal community generates manifestly adequate theories, they must suppose that this ideal community is capable of feats that go far beyond human capacities - indeed, feats that go far beyond the capacities of any conceivable organism. But then why not say that the ideal community is one that observes every observable? This community would produce empirically adequate theories - and this would give us an argument for CE.

What's wrong with manifestationalism?

There are many objections we might raise against M. I want to outline what I regard as a knock-down argument against it. Consider again Frank and his egg. We saw that Frank broke the first egg. So now he goes and out and purchases a second one, which again he intends to put in a box and throw into a volcane. This time, he takes many precautions to avoid breaking the egg, such as wrapping it thickly with bubble wrap. If I accept M, I must be agnostic about the interior of the egg, since I have good reason to believe that this will never be observed.

But now suppose that on the trip up the volcano, Frank gets hungry, and decides he wants to eat the egg. Well, now I have good reason to believe that Frank will observe the interior of the egg, and since our best theories tell us that he will observe a yolk and egg white, I should believe that he will observe a yolk and egg white. Of course, this example can be run in reverse as well, where Frank initially intends to eat the egg, and then intends to throw it into the volcano: in this case, I first believe that he will observe a yolk and egg white, and then I must give up that belief and become agnostic.

This is of course an absurd conclusion, absurd enough in my view that it's enough in itself to remove M from serious consideration. One response to this is to hold that we should remain agnostic about anything that has not yet been observed - even if we have good reason to think that Frank will open the egg, we should remain agnostic about the interior of the egg until he actually does it. But this entails radical scepticism about the future, which is no less absurd; and as I noted earlier, M was supposed to avoid radical scepticism.

Ultimately, it seems to me that A&B fail to show that M is a serious contender. There are very serious, very obvious problems with M, and no plausible arguments in its favour.