|David Hume: the original pro-science troll|
With such polarised debates it is all too easy to sit in one corner and wave your fist at the other. It doesn't get us very far. It is more helpful to figure out exactly what the other side is thinking, and talk about why they think it.
In this case, perhaps the debate hinges on a definition. What do we mean by knowing?
When a scientist says they know something, they mean an idea has been shown to be consistent with observations by somebody trustworthy using a rigorous and reliable method. (Observation, by the way, is not limited to literally seeing things. It includes any reliable method for data collection.)
There is an assumption in this definition of knowing: the idea has to be unambiguously defined, in such a way that its implications can be observed. If the idea itself is so vague and open to debate that no implication of the idea could be observed, then a scientist would say you could never know the idea to be true.
Ideas, however, do not fit neatly into science's box. There are plenty of vague ideas out there, and many of their implications are difficult or impossible to observe with any certainty. Areas of thought such as economics, politics, theology and art contain a mishmash of ideas, some of which can be tested, others of which cannot. Progress in such areas works less like science and more like the law: a continual process of building upon precedent and examining one idea in the light of another. Ideas are rarely right or wrong, just fashionable and unfashionable.
There is also the realm of subjective experience. Whereas science hones in on tightly defined ideas and controlled observations, fighting to remove subjectivity, postmodernism revels in differences of opinion. No two lives are identical, and two people can perceive the same thing in quite different ways. The postmodern position is that no-one's experience is more valid than anyone else's.
When a postmodernist says they know something, they mean an idea is consistent with their own, subjective experience, even if the idea is not fully defined, even if there is nothing they could possibly provide as evidence to support the idea.
This version of knowing is so very far removed from the scientist's version, no wonder there is disagreement over how we can know things. Of course both sides believe they are right, because by their own definitions both sides are right.
So far, so much fence sitting. But it doesn't end there, because the point is not moot: there are implications.
In the real world, there is a crucial difference between the two kinds of knowing, and that is an ethical difference. If you know something in the postmodern sense, it only applies to you, because your knowledge is subjective. If you know something in the scientific sense, because you have removed subjectivity, you can use that knowledge to act in other people's interests.
This is not to deny the presence of subjective components within scientific arguments - you cannot prove something does more good than harm without a subjective definition of good and harm - but you can move an argument on from a simplistic 'I know this is right' to a nuanced 'I know this is right because...' and reduce the level of subjectivity by making as many concrete observations as possible.
As an example, if you know in the scientific sense that vaccinations do more good than harm (defining good as reducing disease and preventing illness and death), you can justify a programme of compulsory vaccination, because the observational evidence is objective and its truth is universal. If you only know it in the postmodern sense, you can only justify vaccinating yourself, because your subjective experience and opinion is yours alone.
So if you think science lovers are arrogant to claim they know the truth, remember that they are only talking about a very specific kind of knowledge, and consider that science's knowledge is universal and objective in a way that other kinds are not.
And if you are a science lover, frustrated with others' disdain for empirical evidence, remember that they have in mind a much more general class of ideas for which evidence is hard to come by, and consider that such ideas, being the stuff of human life, are the basis and the purpose of all scientific enquiry.