Probable cause doesn’t need to be “more likely than not”.
If police rate a 90% chance that either Joe or George have some stolen property in his residence, and they just discovered where Joe is living, they can and should search that location, even though there is a 45% chance at best of finding something.
Judges refuse to attach a number to the probable cause threshold. It seems to be less than 50%, but surely more than 1%.
You’re right that it’s not a numerical percentage. And people don’t calculate like that anyway. Nobody says “there’s a 60% chance he’s the one who did it.” They just figure “yeah, given what I know, he’s probably the one who did it.”
But that’s not what probable cause is about. The question isn’t whether the police thought you did it, or even how certain they were.
Probable cause refers to the evidence on which they based their assessment. The issue is whether the facts they had were sufficient to support their conclusion that you probably did it. If they thought you did it based on a hunch, mere speculation, or curious suspicion, then that’s not probable cause. They need enough evidence to give them good reason to believe it’s so.
So “good reason to believe it” might be another way of phrasing “probable cause to believe it.”
Engineers do think that way; we say “there is a 60% chance this failure will occur”
…yeah you’re working with machines. Things with highly determinisitic automata. Human interaction and motives are much less precise. It’s why psychology doesn’t often deal with hard percentages. Usually more ranges OR general comments.
I agree there’s not much practical benefit to assigning a percentage, because we usually don’t have any practical way to calculate an exact percentage.
But in principle, it should probably be a percentage. Because (AFAIK) the best and most rigorous way that we know how to measure the overall quality of a body of evidence (given lots of data and unlimited time) is to apply Bayes’ Theorem, which would result in a percentage expressing how convincing that evidence should be to a rational observer:
Is “no good” in this case necessarily synonymous with “criminal act,” or can it be anything dubious, but perhaps not illegal?
I find it rather doubtful that many people or the state would consider it acceptable for cops to go around harassing people for legal acts that they personally took offense to.