Brad DeLong is wrong on realism and inference to the best explanation

31 Aug, 2015 at 13:43 | Posted in Theory of Science & Methodology | 4 Comments

Brad DeLong has a new post up where he gets critical about scientific realism and inference to the best explanation:

Daniel Little: The Case for Realism in the Social Realm:

“The case for scientific realism in the case of physics is a strong one…

hqdefaultThe theories… postulate unobservable entities, forces, and properties. These hypotheses… are not individually testable, because we cannot directly observe or measure the properties of the hypothetical entities. But the theories as wholes have a great deal of predictive and descriptive power, and they permit us to explain and predict a wide range of physical phenomena. And the best explanation of the success of these theories is that they are true: that the world consists of entities and forces approximately similar to those hypothesized in physical theory. So realism is an inference to the best explanation…”

“WTF?!” is the only reaction I can have when I read Daniel Little.

Ptolemy’s epicycles are a very good model of planetary motion–albeit not as good as General Relativity. Nobody believes that epicycles are real …

There is something there. But just because your theory is good does not mean that the entities in your theory are “really there”, whatever that might mean…

Although Brad sounds upset, I can’t really see any good reasons why.

In a time when scientific relativism is expanding, it is important to keep up the claim for not reducing science to a pure discursive level. We have to maintain the Enlightenment tradition of thinking of reality as principally independent of our views of it and of the main task of science as studying the structure of this reality. Perhaps the most important contribution a researcher can make is reveal what this reality that is the object of science actually looks like.

Science is made possible by the fact that there are structures that are durable and are independent of our knowledge or beliefs about them. There exists a reality beyond our theories and concepts of it. It is this independent reality that our theories in some way deal with. Contrary to positivism, I would as a critical realist argue that the main task of science is not to detect event-regularities between observed facts. Rather, that task must be conceived as identifying the underlying structure and forces that produce the observed events.

In a truly wonderful essay – chapter three of Error and Inference (Cambridge University Press, 2010, eds. Deborah Mayo and Aris Spanos) – Alan Musgrave gives strong arguments why scientific realism and inference to the best explanation are the best alternatives for explaining what’s going on in the world we live in:

For realists, the name of the scientific game is explaining phenomena, not just saving them. Realists typically invoke ‘inference to the best explanation’ or IBE …

IBE is a pattern of argument that is ubiquitous in science and in everyday life as well. van Fraassen has a homely example:
“I hear scratching in the wall, the patter of little feet at midnight, my cheese disappears – and I infer that a mouse has come to live with me. Not merely that these apparent signs of mousely presence will continue, not merely that all the observable phenomena will be as if there is a mouse, but that there really is a mouse.” (1980: 19-20)
Here, the mouse hypothesis is supposed to be the best explanation of the phenomena, the scratching in the wall, the patter of little feet, and the disappearing cheese.
alan musgraveWhat exactly is the inference in IBE, what are the premises, and what the conclusion? van Fraassen says “I infer that a mouse has come to live with me”. This suggests that the conclusion is “A mouse has come to live with me” and that the premises are statements about the scratching in the wall, etc. Generally, the premises are the things to be explained (the explanandum) and the conclusion is the thing that does the explaining (the explanans). But this suggestion is odd. Explanations are many and various, and it will be impossible to extract any general pattern of inference taking us from explanandum to explanans. Moreover, it is clear that inferences of this kind cannot be deductively valid ones, in which the truth of the premises guarantees the truth of the conclusion. For the conclusion, the explanans, goes beyond the premises, the explanandum. In the standard deductive model of explanation, we infer the explanandum from the explanans, not the other way around – we do not deduce the explanatory hypothesis from the phenomena, rather we deduce the phenomena from the explanatory hypothesis …

The intellectual ancestor of IBE is Peirce’s abduction, and here we find a different pattern:

The surprising fact, C, is observed.
But if A were true, C would be a matter of course.
Hence, … A is true.
(C. S. Peirce, 1931-58, Vol. 5: 189)

Here the second premise is a fancy way of saying “A explains C”. Notice that the explanatory hypothesis A figures in this second premise as well as in the conclusion. The argument as a whole does not generate the explanans out of the explanandum. Rather, it seeks to justify the explanatory hypothesis …

Abduction is deductively invalid … IBE attempts to improve upon abduction by requiring that the explanation is the best explanation that we have. It goes like this:

F is a fact.
Hypothesis H explains F.
No available competing hypothesis explains F as well as H does.
Therefore, H is true
(William Lycan, 1985: 138)

This is better than abduction, but not much better. It is also deductively invalid …

There is a way to rescue abduction and IBE. We can validate them without adding missing premises that are obviously false, so that we merely trade obvious invalidity for equally obvious unsoundness. Peirce provided the clue to this. Peirce’s original abductive scheme was not quite what we have considered so far. Peirce’s original scheme went like this:

The surprising fact, C, is observed.
But if A were true, C would be a matter of course.
Hence, there is reason to suspect that A is true.
(C. S. Peirce, 1931-58, Vol. 5: 189)

This is obviously invalid, but to repair it we need the missing premise “There is reason to suspect that any explanation of a surprising fact is true”. This missing premise is, I suggest, true. After all, the epistemic modifier “There is reason to suspect that …” weakens the claims considerably. In particular, “There is reason to suspect that A is true” can be true even though A is false. If the missing premise is true, then instances of the abductive scheme may be both deductively valid and sound.

IBE can be rescued in a similar way. I even suggest a stronger epistemic modifier, not “There is reason to suspect that …” but rather “There is reason to believe (tentatively) that …” or, equivalently, “It is reasonable to believe (tentatively) that …” What results, with the missing premise spelled out, is:

It is reasonable to believe that the best available explanation of any fact is true.
F is a fact.
Hypothesis H explains F.
No available competing hypothesis explains F as well as H does.
Therefore, it is reasonable to believe that H is true.

This scheme is valid and instances of it might well be sound. Inferences of this kind are employed in the common affairs of life, in detective stories, and in the sciences.

Of course, to establish that any such inference is sound, the ‘explanationist’ owes us an account of when a hypothesis explains a fact, and of when one hypothesis explains a fact better than another hypothesis does. If one hypothesis yields only a circular explanation and another does not, the latter is better than the former. If one hypothesis has been tested and refuted and another has not, the latter is better than the former. These are controversial issues, to which I shall return. But they are not the most controversial issue – that concerns the major premise. Most philosophers think that the scheme is unsound because this major premise is false, whatever account we can give of explanation and of when one explanation is better than another. So let me assume that the explanationist can deliver on the promises just mentioned, and focus on this major objection.

People object that the best available explanation might be false. Quite so – and so what? It goes without saying that any explanation might be false, in the sense that it is not necessarily true. It is absurd to suppose that the only things we can reasonably believe are necessary truths.

What if the best explanation not only might be false, but actually is false. Can it ever be reasonable to believe a falsehood? Of course it can. Suppose van Fraassen’s mouse explanation is false, that a mouse is not responsible for the scratching, the patter of little feet, and the disappearing cheese. Still, it is reasonable to believe it, given that it is our best explanation of those phenomena. Of course, if we find out that the mouse explanation is false, it is no longer reasonable to believe it. But what we find out is that what we believed was wrong, not that it was wrong or unreasonable for us to have believed it.

People object that being the best available explanation of a fact does not prove something to be true or even probable. Quite so – and again, so what? The explanationist principle – “It is reasonable to believe that the best available explanation of any fact is true” – means that it is reasonable to believe or think true things that have not been shown to be true or probable, more likely true than not.

I do appreciate when mainstream economists like Brad make an effort at doing some methodological-ontological-epistemological reflection. On this issue, unfortunately — although it’s always interesting and thought-provoking to read what Brad has to say — his arguments are too weak to warrant the negative stance on scientific realism and inference to the best explanation.


  1. Brad concluded:

    “There is something there. But just because your theory is good does not mean that the entities in your theory are “really there”, whatever that might mean…”

    I have some sympathy with this view.

    Quantum mechanics is our latest and greatest but it might not be our last.

  2. Who knows what’s “out there”?

    For instance, It might be that the world circumscribed by classical economics (perfect knowledge, no time) exists, but given our sensory and cognitive limitations, we have no access to it.

    After all, what we “know” is what our senses bring to us piecemeal, then integrated into a seeming continuum, by our brain – our only point of reference being a prior memory.

    The notion of a Platonic cave dweller casting shadows might even be too sanguine – the cave may be completely dark.

  3. I do not think Brad’s comment actually contains the fault you attribute to it. He’s very clear in his endorsement of reality as real — it is just that he follows physicists in the reductionism of quantum physics:

    “. . . if you ask physicists whether the entities of Einstein’s theory are really there, they will say: “Of course not: Those entities do not satisfy the quantum principle. We very strongly believe that what we see as particles moving along geodesics in a space-time curved by the mass-energy-pressure density is an approximate model–a very good approximate model–to emergent properties that are produced by some very different underlying set of real entities that are governed by the quantum principle.”

    That seems to me like a very clear commitment to a science of real entities to me.
    The difficulty may be that Daniel Little says, “inference to the best explanation” (which gets Lars Syll to nod) even while the rest of what Little says seems to be inexplicably like a Platonic faith in the super-reality of nomological machines. What Brad DeLong appears to me to react to, in Little’s remarks, is the implication that the Idea embodied in the Nomological Machine is Real in some Platonic sense: our ideas of the world are real, while observable phenomena are mere imperfect shadows.
    Einstein’s Theory of Special Relativity and its slightly younger, bigger brother, the Theory of General Relativity are not very far removed from the (non-Euclidean) geometry he used to derive them. Those theories are, essentially, maps. To say, as DeLong summarizes it, that “matter and energy moves along geodesics in space-time” is describing features of a map. It should hardly be heresy to say that the map is not the territory. You can recognize that the map is not the territory, and still think the territory is real. That, it seems to me is Brad’s position: Einstein’s Relativity constitutes some really good maps (granting various fudge factors), but investigation of the nature of the territory must follow other (quantum) lines.

  4. For starters, this post confuses explanation of physical phenomena with explanation of social phenomena. The key difference here is that explanations in the physical sciences do not change the reality of the event being examined; and only true explanations can be applied in the practical sense. The social sciences however involve an abrupt change when an explanation is true: the phenomena in question are changed by correct conceptualizations or true explanations. This does not happen with physical phenomena – they do not change because of your explanation. The role of feedback between social phenomena and explanations means that explanation is a never-ending quest and there is no absolute truth because new concepts are always necessary to explain phenomena which change because of the recent explanations.

    Furthermore, our beliefs, or notions of absolute truth, always contain some degree of error under new conditions. Beliefs, like truth, are always matters of degree, or in gradations. This is true in both natural and social science. We must always consider our explanations fallible at least to the extent that a new circumstance may emerge in which our concepts do not fit, although we may believe that they do! So, error is everpresent.

    We should be critical of realism in the social sciences but we should also recognize that our conceptualizations must always be reworked because our social reality changes with each new conceptual framework. In economics, we see this occurring with the latest neoliberal reforms which are always trying to buy time to make the social reforms of entire populations through debt calculations in the hope that at some point everyone’s work role and consumption pattern will meet their preconceptions.

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