It’s salvation of a kind: our apparently irrational quirks start to make sense when we think of reasoning as serving the purpose of persuading others to accept our point of view. And by way of positive side effect, these heated social interactions, when they occur within a scientific community, can lead to the discovery of the truth.

And what about scientists’ prejudices? Clearly, social values should never count as evidence for or against a particular hypothesis — abhorrence of the death penalty does not count as data against its crime-deterrent effects. However, the philosopher of science Heather Douglas has argued that social values can safely play an indirect role in scientific reasoning. Consider: The greater we judge the social costs of a potential scientific error, the higher the standard of evidence we will demand. Professor A, for example, may be troubled by the thought of an incorrect discovery that current levels of a carcinogen in the water are safe, fearing the “discovery” will cost lives. But Professor B may be more anxious about the possibility of an erroneous conclusion that levels are unsafe, which would lead to public panic and expensive and unnecessary regulation.

Both professors may scrutinize a research paper with these different costs of error implicitly in mind. If the paper looked at cancer rates in rats, did the criteria it used to identify the presence of cancer favor over- or under-diagnosis? Did the paper assume a threshold of exposure below which there is no cause for concern, or did it assume that any level of exposure increases risk? Deciding which are the “better” criteria or the “better” background assumptions is not, Ms. Douglas argues, solely a scientific issue. It also depends on the social values you bring to bear on the research. So when Professor A concludes that a research study is excellent, while Professor B declares it seriously mistaken, it may be that neither is irrationally inflating or discounting the strength of the evidence; rather, each is tending to a different social concern.

Science often makes important contributions to debates that involve clashes of social values, like the protection of public health versus the protection of private industry from overregulation. Yet Ms. Douglas suggests that, with social values denied any legitimate role in scientific reasoning, “debates often dance around these issues, attempting to hide them behind debates about the interpretation of data.” Professors A and B are left with no other option but to conclude that the other is a stubborn, pigheaded excuse for a scientist.

For all its imperfections, science continues to be a stunning success. Yet maybe progress would be even faster and smoother if scientists would admit, and even embrace, their humanity.