Should you carry an umbrella on a cloudy day? Can you wait till the chance of rain is either 100% or 0% to decide? Day-to-day choices—and the big choices, too—rest on imperfect knowledge. How much certainty we demand depends on what’s knowable and how much it matters.
Long ago, I was married to a soldier in the Army Security Agency. Though I wasn’t privy to his top-secret training, I suspect that’s where he learned labels for different degrees of certainty or validity. A-val meant certain, B-val probable, C-val perhaps fifty-fifty, D-val possible. These terms entered my vocabulary for historical research and everyday life.
The standard of evidence in criminal prosecutions is A-val, beyond a reasonable doubt. In civil suits it’s B-val, preponderance of the evidence. Lack of certainty isn’t cause for paralysis or cynicism. Often the best we can do is estimate likelihood, compare the risks of getting it wrong in one direction versus the other, and move forward.
I'm a historian who writes novels and literary nonfiction. My home base is Madison, Wisconsin.