Whilst revising relational databases I came across this point regarding functional dependencies:

Quote

Given some allowable instance r of R and an FD f, we

can try to use r to check if f does not hold over R, but

we cannot normally use r to check if f does hold over R.

can try to use r to check if f does not hold over R, but

we cannot normally use r to check if f does hold over R.

I'm sure there is a formal name for this. Not just for this particular case, but for when you can disprove an entire theory by proving it wrong in a single case, but cannot prove it to be true by proving it once.

Sorry if this is terribly phrased, but it's really bugging me that I can't think of the correct term.

Thanks in advance,

Sam