If Evidence Neutrality (EN) is true, it is presumably true everywhere. One way to argue against it then is to argue that it doesn’t hold in other subjects. And that’s what Williamson does. He argues that it doesn’t hold in particular in science.

bq. If Evidence Neutrality psychologises evidence in philosophy, it psychologises evidence in the natural sciences too. But it is fanciful to regard evidence in the natural sciences as consisting of psychological facts rather than, for example, facts about the results of experiments and measurements. When scientists state their evidence in their publications, they state mainly non-psychological facts (unless they are psychologists); are they not best placed to know what their evidence is?

If this were a true description of the position of evidence in science, it would be a problem for EN. But it isn’t. EN doesn’t psychologise evidence in science, it _institutionalises_ it. Let’s recall the original statement of EN.

bq. [W]hether a proposition constitutes evidence is in principle uncontentiously decidable, in the sense that a community of inquirers can always in principle achieve common knowledge as to whether any given proposition constitutes evidence for the inquiry. (Emphasis added)

Here’s one way to preserve EN in a field. Adopt some standards for something being evidence in that field, standards that are in practice (if not always in theory) decidable. Then take questions about whether those standards are good standards to belong to another field. That is, take it that people who are questioning the standards, questioning whether these standards genuinely generate evidence, to be outside the community in the sense relevant to EN. They might of course be part of another intellectual community, but they aren’t part of this community. That way we can preserve EN within every given community.

Compare a principle we might call Foul Neutrality (FN) governing a sport. It’s pretty important for playing football that we have a quick method for deciding what’s a foul and what isn’t. And this must be decidable independent of one’s interest in the game. We don’t get FN by psychologising fouls; we get it by having referees. The referees could be wrong, and indeed we could have interesting projects about improving the quality of referees. But when we engage in that project we’ve stopped playing football. The community of footballers (as such) satisfies FN because it’s part of being in that community that we take the referee’s word as final.

Science isn’t like football in that it requires absolute respect of the referees judgment. But it is frequently true that the project of using methods or devices to produce evidence is quite distinct from the project of evaluating whether those methods or devices are good. And we can sensibly individuate communities by looking at which methods they take as given. The short version of my response to this argument is that that’s really how science works; i.e. that science consists of communities so individuated. Each community has a refereeing institution. Or, at least, it is how it works in the vast majority of cases. In cases where the refereeing institutions break down, where there isn’t some other community to serve in effect as referee for your community, then we might have to fall back on psychological states. But EN doesn’t systematically psychologise evidence in science.

We might think that evidence must consist of facts measured rather than something about their measurement, because those are the kinds of things we can submit to statistical testing. But that argument, if it works, proves too much. Williamson’s initial description of scientific evidence was that it consisted of “the results of experiments and measurements”. But that’s ambiguous between two readings. On the first, scientists just state the outcomes of their measurements. That is the kind of thing that you can do statistical analysis on. On the second, they state the results of the measurement, and describe what kind of measurement it is. And that’s, I think, the true reading. At least for results of any interest, you have to describe how you got them, as well as what you got. But you can’t do statistical analysis on a description of a kind of measurement. So it isn’t true that all scientific evidence consists of things you can plug into mathematical equations.

On the other hand, this picture of scientific practice does seem to support the institutional picture of evidence. Why is it that we report the methods as well as the result? One simple answer is that it is settled (relative to the kind of science we’re engaged with) that using that method produces scientific evidence. That’s not to say that the method is beyond dispute. It might be that some other science studies the workings of the very machines that a particular science takes for granted in their operations. It’s merely to say that this science has approved the method in question.

We can see this even more clearly if we look at engineering settings rather than science settings. Imagine we’re working on a bridge construction project, and we need to know the density of some concrete. We’ve got a machine that measures concrete density, so we use it and, assuming the answers are plausible, we’ll take those answers as given. Evidence Neutrality will be ssatisfied because we’ll agree to use the machine. Of course, the only reason we trust the machine is that there is someone, typically someone else, whose job it is to test the machine on a regular basis, and service it, or have it serviced, if it isn’t, and although we might not know the details of how this process works, we’ll have a nice certificate saying the machine is in good condition to use. Now the folks who calibrate machines like this aren’t perfect, so there are other people whose job it is to audit them on a regular basis. And auditors aren’t perfect either, so there will be some body, perhaps a certification body, that oversees them. A positive mark from an auditor only licences a calibrator to approve a machine if the auditor is in turn certified. The board itself may need to be checked, so maybe it will have a board, perhaps including representatives of people like bridge builders who use the machines that we’re all interested in.

The crucial point about this story is that at every stage in the process, EN is satisfied. It is similar, I think, in sciences, though the structure is more fluid. Just which sciences will validate the use of the measurement techniques in other sciences is not as straightforward as in engineering. And the precise boundary between questions that are internal to a given science and questions external to it will change over time. When many questions central to the science start to turn on a particular kind of question about measurement, then those measurement questions may become part of the science. (For instance, if experimental philosophy really takes off, perhaps questions about survey design will be regarded as philosophical questions in the future. More prominently, in recent years questions about the behaviour of satellites have become part of climate science because of the importance of satellites to climate measurement.) But still the broad structure is fairly similar.

The big difference between science and engineering is what happens at the end of the process. The way I described the bridge building case was that eventually, the people responsible for checking the activities of others were the very people (or at least the representatives of them) who were being watched over to start with. That obviously isn’t what happens in science. We don’t check the activities of (say) particle physicists by putting together a board of psychiatrists, nutritionists, economists etc. How might we satisfy EN in basic physics?

Two obvious answers spring to mind. One, either common sense or philosophy tells us that we can take perceptual evidence as given. So even in fundamental physics we can individuate the community in such a way that those who are raising sceptical doubts are doing something else, namely philosophy.

The other answer is that we might take scientific evidence, at the most fundamental level, to be psychological states. Certainly it isn’t uncommon for _philosophers_ of physics to take the role of physical theory to explain our observings. That’s part of why we’ve ended up with such psychologically flavoured interpretations of quantum mechanics, from the Copenhagen interpretation to the many minds interpretation. Perhaps that’s just philosophers bringing in bad philosophical prejudices, but it seems like we _can_ do science respecting EN. That’s because EN mostly is satisfied by the institutional structure of science, and when it isn’t, it doesn’t seem to destroy science to take some evidence to be psychological. So there isn’t an argument from science against EN.