To make a political decision, you sort through the evidence to find the facts that are most relevant to the issue—and “relevant,” please note, is a value judgement, not a simple matter of fact. Using the relevant evidence as a framework, you weigh competing values against one another—this also involves a value judgment—and then you weigh competing interests against one another, and look for a compromise on which most of the contending parties can more or less agree. If no such compromise can be found, in a democratic society, you put it to a vote and do what the majority says. That’s how politics is done; we might even call it the political method.
That’s not how science is done, though. The scientific method is a way of finding out which statements about nature are false and discarding them, under the not unreasonable assumption that you’ll be left with a set of statements about nature that are as close as possible to the truth. That process rules out compromise. If you’re Lavoisier and you’re trying to figure out how combustion works, you don’t say, hey, here’s the oxygenation theory and there’s the phlogiston theory, let’s agree that half of combustion happens one way and the other half the other; you work out an experiment that will disprove one of them, and accept its verdict. What’s inadmissible in science, though, is the heart of competent politics.
I love the term political reasoning. I’ll try expand on it in an upcoming post.