Why Empiricists should Endorse Modalities (2) Scientific Rationality

In the previous post, I explained why, assuming that there is necessity in the world, relations of necessity are perfectly knowable on the basis of experience, without any recourse to abductive reasonning. That certainly works in favour of an endorsement of natural modalities for the empiricist: at least, epistemic arguments against it are not conclusive. But still, an empiricist could resist this kind of commitment by assuming that there is no necessity in the world from the start. She could interpret modal discourse in a pragmatic way, rather than assume that modal statements have truth values. In this post, I want to explain why she shouldn't.

As I said in the previous post, I don't think that the existence of necessity in the world itself (as opposed to relations of necessity if there is necessity in the world) can be confirmed or disconfirmed by experience. However, no position really comes without some general metaphysical framework, and this includes all empiricist positions: the idea that all knowledge comes from experience is not itself confirmed or disconfirmed by experience. The idea that our theories will continue to be empirically adequate in the future is not confirmed or disconfirmed by experience. The empiricist is only willing to assume the minimum necessary, and to refrain from speculations. One could frame this as some kind of transcendental argument: we need some basic assumptions to make sense of the world, but we shouldn't assume more.

This is exemplified by van Fraassen's defense of constructive empiricism. He does not say that his position is itself confirmed by experience, but he rephrases empiricism as a position about the aim of science, as a collective endeavour: its aim, according to van Fraassen, is to produce empirically adequate theories (not true theories). A scientist can well be a realist, but needs not be to be a good scientist. However, a scientist must at least assume that our theories are empirically adequate, and will continue to be in the future. Now if one thinks that scientific practice is a rational activity, one should also believe that our best theories are empirically adequate. This is a minimum.

I think this is the correct way of thinking about epistemological positions. But I think that it supports modal empiricism rather than constructive empiricism.

Why empiricists should endorse modalities (1): modal knowledge

Let us take stock. In the posts so far (linked below in order),

• I presented modal empiricism: the view that our best scientific theories are empirically adequate for all possible situations to which they would apply.
• I detailed the conception of empirical adequacy on which the position rests. It is not cast in terms of a model of the universe, as usually, but in terms of situations to which different models apply, and, I think this conception is more connected to scientific practice than the usual ones.
• This conception of empirical adequacy does not commit us to modal empiricism, but I explained how modal empiricism is able to answer the no-miracle argument, while retaining the advantages of empiricism when it comes to theory change.
• Finally, I explained why, according to me, scientific realism is misguided: it rests on (meta-)abduction for its justification, but abduction, however central it is in scientific practice, is not a principle of justification, but a strategic device to select good hypotheses: hypotheses that we should test first, that is. It doesn't exempt us from further empirical tests if we want to justify these hypotheses. But scientific realism cannot itself be tested empirically.

What makes modal empiricism a version of empiricism, not of scientific realism, is that in contrast with realism, the modalities to which it is committed are arrived at by induction on possible situations, not by abduction. Relations of necessity are no explanations to regularities, but regularities extended to the possible.

Against abduction

Abduction (or "inference to the best explanation") is the cornerstone of scientific realism. There are always many different theories, or hypothesis that could account for some given phenomena, but scientists make their choice on the basis of non-empirical criteria, such as simplicity: they choose the best explanation. According to a realist, this means one likely to be true. This, in essence, is abductive reasoning: an inference from non-empirical, explanatory virtues to truth, or to likelihood. Furthermore, the realist claims that her position, that our best scientific theories are approximately true, is itself the best explanation to their predictive success. That's what we could call a meta-abduction: a justification of abduction (best explanations are true) by means of abduction (that best explains their success, so it's true). So it's clear that abduction is essential to realism, perhaps its definite characteristic. But is abduction a valid form of inference?

Is empirical success a miracle?

In the previous post, I detailed my conception of empirical adequacy: a theory is empirically adequate if for every model of the theory, for all situations to which the model would apply, the model would make correct predictions. Depending on the range of situation we consider (situations actually experimented, actual situations we could experiment in principle...) on can derive different versions of empiricism. Modal empiricism is the view that our theories are empirically adequate for all possible situations.

In this post, I would like to explain why modal empiricism can respond to the no-miracle argument for scientific realism, and why it is not threatened by a meta-induction argument. But before that, we must examine the different kinds of induction that are involved in our definition.

Empirical Adequacy: a Proposal

In the last post, I criticised van Fraassen's definition of empirical adequacy. According to van Fraassen, a theory is empirically adequate if it has at least one model such that all observable phenomena fit inside (they correspond to the empirical substructures of the model). My criticisms were the following: it rests on a problematic distinction between observable and unobservable, it does not take into account interventions and manipulations, which are central in scientific experimentation, and it refers to an hypothetical model of the universe, which is unnecessary and disconnected from scientific practice.

Can we do better? I think we can if we directly refer to scientific experimentation instead of coming up with an abstract reconstruction of empirical adequacy. Empirical adequacy should simply be framed in terms of the good predictions of models when they apply to various situations. Thus I suggest the following definition:

A theory is empirically adequate exactly if, for all its models, and for all concrete situations in the world, if the model applies to the situation, then its predictions are correct.

Here it is: that's a pretty simple definition. Now, of course, I need to expand a bit what all this means. This is the aim of the present post. But let me begin with an illustration.

Take as a concrete situation the evolution of the solar system during a certain period of time. A Newtonian model of the solar system applies to this situation if it correctly describes the planets and the sun, with their respective initial positions and masses. It makes good predictions if the evolution of the position of planets in the model correspond to the positions that we could observe in this situation. If this is so, then our model of the solar system is empirically adequate for this situation. If all models of the theory that we could apply in the world are empirically adequate for all situations to which they apply in the world, then our theory is empirically adequate.

I will now explain in more details what I mean by situation, application and prediction.

What is Empirical Adequacy? Against Observability and the Model of the Universe.

In the last post, I explained how I conceive of physical theories: roughly, a vocabulary and axioms, from which we build models applicable to particular types of situations. Models can be mapped to concrete situations in the world, and we can compare their predictions to data models extracted from these situations. From this picture, we can ask: what is it, for a theory, to be empirically adequate?

Van Fraassen, who is one of the main contemporary defenders of empiricism, proposes a definition of empirical adequacy which is the following:

"A theory is empirically adequate exactly if what it says about the observable things and events in this world, is true—exactly if it ‘saves the phenomena’. A little more precisely: such a theory has at least one model that all the actual phenomena fit inside. I must emphasize that this refers to all the phenomena; these are not exhausted by those actually observed, nor even by those observed at some time, whether past, present, or future."

This definition dates back to his 1980 book "the scientific image" (You can find a similar one in a footnote of his 1989 "laws and symmetry"). What he means by "fit inside" is explicated later in the book in terms of isomorphism between data models and the "empirical substructures" of theoretical models. I think it's not the right way to understand empirical adequacy for several reasons, and although his notion of "fit inside" was challenged by some authors, who proposed more sophisticated accounts, this is hardly my main point of contention.

How do scientific theories represent the world? The semantic view reconsidered.

Before to wonder whether scientific theories are correct description of reality, or if they only "save the phenomena", one should better be clear about what scientific theories are, and how they are confronted to experience. In this post, I discuss the so-called "semantic conception of theories", then I present my own synthesis of how theories and their empirical confrontation should be construed, and in a final note, I give some very general options on how theories would represent reality.

Structural realism or modal empiricism?

Welcome to this new blog dedicated to the philosophy of science. I already have two blogs, but they're in French, so I decided to make a new one in English. Not that I don't like to write in French. It's a lot easier: my style is more fluid and precise than in English. I also like the idea of keeping my home language alive, especially in philosophy, as English is increasingly becoming the only language in town. But having a blog in English will allow me to share my thoughts with a wider audience, or so I hope. (Please excuse my language mistakes and correct me any time in comments, that's how I'll improve!).

One of my purpose here will be to share in an informal way the content of my PhD dissertation, which I'm currently writing. The dissertation mainly talks about epistemological issues in science, with a little metaphysics. To be precise, I defend a position in the debate on scientific realism, which I dubbed "modal empiricism". I think it's an original position (although the term appears with the same intended meaning in a chapter by Giere in "Images of Science: Essays on Realism and Empiricism", 1985). The position can be expressed in more than one way, but here is one: our best scientific theories are correct descriptions of the relations of necessity between our observations and interventions. Here is another one: all that we know is that our theories are empirically adequate, but the empirical content of our theories is modal: it's about possible experiences.

There is a lot to say, but I think that this position has lots of virtues. For a start, let me say a word about how I came to defend it. The readers familiar with structural realism and Newman's objection can skip to the last paragraph of this post.