Hypotheses and Falsifiability according to Karl Popper
It’s easy to find confirmations of nearly any theory – if all we look for are confirmations.
Confirmations of a theory should count only if they are the result of risky predictions, and if they appear despite genuine efforts to refute the theory.
No number of confirmations of a theory is sufficiently large to prove it, but only a single refutation is sufficient to disprove it.
Every good scientific theory is a prohibition, i.e., it forbids certain things from happening. The more it forbids, the better it is.
A theory that is not refutable by any conceivable experiment is non-scientific. Irrefutability is not a virtue; it is a vice.
The strict criterion for a theory being scientific is falsifiability (not that it is false, but that it can be proven to be false.
Nathan's Addenda
If two competing hypotheses cannot be distinguished by any conceivable experiment, then they are scientifically equivalent.
We can come no closer to the truth than our own imaginations will allow.