Varieties of Evidence Redux

About a year ago, I posted three blog posts here, arguing that scientific evidence serves a more complex and dynamic set of functions in scientific inquiry than simply supporting hypotheses.  I've finally manage to work the idea out in a form that I'm satisfied with:

The Functional Complexity of Scientific Evidence (Draft)

I'm especially indebted to the commenters on this blog for the content of section 6, including Thomas Basbøll, Greg Frost-Arnold, Gabriele Contessa, and Eric Winsberg.  (I hope I've appropriate credit where credit is due there.  I was a bit stymied in how exactly to refer to a conversation we had on the blog, and so made the acknowledgments there fairly general.  Advice on that point is welcome.)

I hope I've managed to present it in a compelling way and answer the objections in a satisfactory way, even though I'm sure many traditionalist won't be convinced.  The goal in this paper is to motivate the need for more complex, functionalist, dynamic model of evidence in contrast with the oversimplification of the traditional-type model, to set out in detail such a model, to illustrate it with an example, and to reply to some basic objections.  I've got a second paper in progress which applies the basic framework to a variety of problems of evidence, from theory-ladenness and the experiment's regress to "evidence for use" and evidence-based public policy.  My central claim there is that this apparently diverse set of problems all share a set of assumptions, and the strongest way to solve them all is to adopt the dynamic evidential functionalism that I've laid out in this first paper.

One reason that I needed to whip this paper into shape is that I'm presenting on the topic of the sequel at the Pitt workshop on scientific experimentation.  Getting this in final form is part of finishing up that paper.  The working title there is "From the Experimenter’s Regress to Evidence-Based Policy: The Functional Complexity of Scientific Evidence."

If anyone gets a chance to look at the paper, I'd appreciate any comments, here or via email. 

The Epistemic Role of Suggestive Evidence

This'll be my last post on this particular subject for a while, since this project has to go on the back burner for a while as certain other deadlines loom.

As Eric Winsberg says in reply to my first post,

suggestion is a causal relation, support is not. Whether E suggested H is a matter of historical fact indexed to a particular time. whether A supports B is a very different kind of fact; one which might vary over time, etc.

...

A dream or a blow to the head might very well suggest a hypothesis, but they are not evidence. the kinds of examples where we are inclined to call the thing that suggests a hypothesis "evidence" are the ones where the thing also supports the hypothesis.

In other words, insofar as suggestion is independent of support, it is purely a causal relationship. Now, I'm disinclined to admit a complete epistemic/causal dichotomy, as I think it is well-established that we rely on all kinds of causal relations in our epistemology. But I also think that suggestion has clear epistemic features independent of actual causal events. As I said above, suggestion is an ability in scientists that is trained, it is something we evaluate agents as being better and worse at. Making good suggestions is a kind of agential epistemic virtue. It's also not entirely the case that "Whether E suggested H is a matter of historical fact indexed to a particular time." Whether E is taken to suggest H is such a historical fact, but so is whether it is taken to support H. On the other hand, we can, looking back at the historical case, verify or evaluate whether E suggests H (this is probably clear to anyone who has had that "detective story" experience when reading the history of science, coming up with the hypothesis "before" the scientist), just as we can do with support. We can also identify alternative hypotheses the evidence suggests that went unrecognized.

Now, I won't deny that it is possible in some degree to re-construct many cases of suggestion as cases of support; rational reconstruction can be a powerful tool for fitting square pegs in round holes. However, I would argue that doing so is not only fairly unilluminating for understanding the practice of science, but also that it provides succor to skeptical arguments. It is my eventual hope to argue that it is precisely such reductive, mono-functional, uni-direcitonal accounts of evidence as support which are responsible for skeptical worries about, e.g., theory-ladenness and the experimenter's regress. Such skeptical worries can (and are) ignored, but the common refrain that skeptical problems are insoluble and irrelevant ignores the fact that the problem is internal to these common accounts of evidence. Compelling versions of anti-skepticism have always been accompanied by alternative theories of evidence in which the "E supports H" relation is supplemented by other epistemic functions. (e.g., Quine's view that treats evidence-statements and theoretical statements as symmetrically related and judged on their functional fitness in accommodating experience, for all its problems, provides an internal reason for saying that skeptical worries ask too much).

Examples of Suggestive Evidence

I argued in my last post and in the lively discussion in the comments that evidence has a wider variety of epistemic functions that is commonly appreciated and that those epistemic functions are not reducible to the "support" function. In other words, I want to characterize the essential features of inquiry not as an attempt to gather information that confirms or contradicts some theory of hypothesis, but rather as a complex, multi-phase, multi-directional set of interactions between evidence and theory, as well as problem-statement and other elements.

To be clear, I'm defining evidence in a very broad way: observationally or experimentally generated information about empirical particulars, including not only "raw data" but also models of data, basic interpretations of the data, and even rather generic statements about the phenomena. What I don't mean is what Greg Frost-Arnold suggested in his comment: that we reserve "evidence" for that set of data or information which is settled at the end of an inquiry as figuring in the "support" relation. That is, Greg suggested a dichotomy between "data," which serves all the complex roles I'm interested in, and "evidence," which is the end-product serving the traditional "support" role. While we can go far on this amendment to my argument, I don't ultimately accept it. A basic part of the problem is that philosophers tend to cut off the product from the process and then focus exclusively on the former. This is one of the cases where I think the best way to avoid the strategy is to insist that the product cannot be treated independently. Thus, the broader sense of evidence.

One forceful objection to my view (pressed especially by Thomas and Gabriele Contessa in comments) is that the only way evidence could serve any other function is derivative on and reducible to its function of supporting. Let's focus on my claim that evidence not only supports hypotheses but also suggests them. I think this works in the following way: the inquirer, faced with a problematic situation, surveys the preliminary evidence, which allows them to generate first an attempt to state the problem to be investigated and subsequently a hypothesis for solving the problem. In scientific inquiry, the ability to suggest hypotheses worth investigating further depends heavily on training and "tacit knowledge," but it is, I think, just as essential in naive, commonsense inquiry.

Let's look at some examples:

1. Consider a child attempting to grow flowers in a flower bed. She's rather upset by the fact that some of the flowers aren't growing very well, while those in a small part of the bed are growing rather well. Looking carefully at the garden during the day, she notices that the small part of the garden with healthy flowers gets full sunlight, whereas the other parts are shaded by the fence or a nearby tree. This suggests to her that maybe the difference is due to the amount of sunlight the plants receive. (Probably the initial observations suggest several other hypotheses as well, but she decides to choose this one.) Now, in order to really support her hypothesis, she'll have to do an experiment. . . .

2. A case from John Dewey's How We Think (1910) of inquiry involving an experiment:
   

   In washing tumblers in hot soapsuds and placing them mouth downward on a plate, bubbles appeared on the outside of the mouth of the tumblers and then went inside. Why? The presence of bubbles suggests air, which I note must come from inside the tumbler. I see that the soapy water on the plate prevents escape of the air save as it may be caught in bubbles. But why should air leave the tumbler? There was no substance entering to force it out. It must have expanded. It expands by increase of heat or by decrease of pressure, or by both. Could the air have become heated after the tumbler was taken from the hot suds ? Clearly not the air that was already entangled in the water. If heated air was the cause, cold air must have entered in transferring the tumblers from the suds to the plate. I test to see if this supposition is true by taking several more tumblers out. Some I shake so as to make sure of entrapping cold air in them. Some I take out holding mouth downward in order to prevent cold air from entering. Bubbles appear on the outside of every one of the former and on none of the latter. I must be right in my inference. Air from the outside must have been expanded by the heat of the tumbler, which explains the appearance of the bubbles on the outside. . . . (pp. 70-71, emphasis added)

3. A case from John Snow's work on cholera in the 19th Century: various kinds of evidence has shown that the effluvial hypothesis for the transmission of the disease was unworkable. From reports and his observation of cholera patients, Snow saw that the pathology of the disease began with intestinal symptoms, rather than symptoms of systematic infection such as fever. This suggested the hypothesis that some morbid material ejected from sick patients was subsequently ingested by those who became infected (and several of the histories of Snow describe it in just this way, that the pathology along with other facts suggested the hypothesis about transmission). Snow then went on to support hist hypothesis by certain epidemiological evidence. . . .

Now, I guess we can't deny that suggestion is a real process going on in inquiry. What is at issue is whether it is both distinctive and epistemic, which I'll attempt to defend in a subsequent post.

The Varieties of Evidence

One of the things that seems to me to distort a lot of the discussions of evidence in philosophy of science (and related areas of epistemology) is an over-simplification of the role of evidence in science and inquiry. In particular, many accounts tend to treat evidence as mono-functional, where the only important function evidence plays is support. The nature of that support relation might vary from account to account (Bayesianism, falsification, inductivism, etc.), but many accounts agree that this is how evidence should be understood.

In contrast, I think we can point to a number of equally essential roles that evidence plays in inquiry. When first setting out to investigate the problem, early observational evidence can help locate or specify the problem. When you have an outbreak of disease, or an unexpected astronomical event, you first have to gather as much evidence about the nature of the problem as possible, before you can pose hypotheses or explanations for testing / support. Gathering evidence can also actually suggest hypotheses. A first look at the evidence suggests that this problem might be best analyzed by Fourier analysis, or a simple retrospective study design, or spectral analysis, etc., or by hypothesizing that the disease is malaria, that the new object in our telescope is a type of quasar, etc. Gathering evidence can also help with the elaboration of a hypothesis, specifying, clarifying, or improving it. And not only can it provide support for a hypothesis by testing or confirming its predictions, but experimental testing can be understood as a type of testing by application. If we understand experiment as a kind of intervention on the basis of a theory or hypothesis, then it is really a type of application of the hypothesis to some situation (often a highly controlled one).

So, to sum up, a (probably partial) list of the various functions of evidence: locating the problem, suggesting a hypothesis, elaborating the hypothesis, supporting the hypothesis, and testing it by application. Probably I should say something about helping specify initial conditions, too, though I'm not sure everyone would be willing to call that "evidence."

One way that idealizing evidence as mono-functional, focusing exclusively on the support relation, might go wrong, is the tendency to worry overmuch about the independent status of evidence; i.e., if evidence is to be judged solely by its suitability for providing firm support, then all of the problems of the "empirical basis" start to rear their ugly heads. I suspect that when we have a more complex picture of the functions of evidence, we can use it to develop a multi-scale analysis of the functional fitness of that evidence, which gives as a way of assessing the adequacy of it to stand as evidence.

Scientific Realism and Epistemic Justification

As far as I can see, much of the recent scientific realism debate revolves around the question of whether or not we are epistemically justified in believing our best scientific theories (or parts thereof) to be (approximately) true. In light of this, I've always found quite surprising that philosophers of science seem to be by and large uninterensted in the debates among epistemologists concerning epistemic justification. Among the few exceptions that I can think of are those scientific realist (such as Richard Boyd and Stathis Psillos) who more or less explicitly take an externalist/reliabilist stance on epistemic justification. However, I can hardly think of any scientific realist who takes an explicitly internalist/evidentialist stance. Yet, I don't see why an internalist/evidentialist view of justification wouldn't suit the purposes of (some) scientific realists. Do you think this is just an accident? Or do you see any serious reasons for a scientific realist to think s/he is better off being an externalist about epistemic justification (independenlty on who is right between internalists and externalists)?