In UK civil trials, it is said that
- The burden of proof is on the claimant.
- The case will be decided ‘on the balance of probabilities’.
Are these assertions consistent? Based on the second statement, one might think that the outcome of a case will depend on whether it is more likely than not (>50%) or less likely than not (<50%) that the claimant’s allegation is correct (based on the relevant evidence). But if that is true, I don’t see how the claimant has any special ‘burden’ that they need to discharge. Sure, in order for the claimant to win, the relevant decision maker (let’s say it is a judge) needs to think that it is more likely than not that the claimant is right. But equally, in order for the defendant to win, the judge needs to think that it is more likely than not that they (the defendant) are right. So the situation is entirely symmetric!
Update: as some have commented, the claimant may lose if the judge thinks that the probability is exactly 50%. If you think, for example, that the judge’s assessments should be restricted to integer percentages (0%, 1%, 2%, etc.), this means that the claimant wins if the probability is 51% or higher, and loses if the probability is 50% or lower. This situation is very slightly asymmetric; but only very slightly! And if the judge can make more nuanced judgments (no longer restricted to integers), the asymmetry shrinks.