"2 theories, same experimental predictions, can one fail but not the other ?" (above was intented to be the title, got truncated) Let’s say we have 2 physical theories, call them A and B, that make the same experimentally verifieable predictions. But they are based on different postulates. And they calculate their stuff in different ways.(<-sorry for such an inaccurate description in that sentence) I would have assumed that some theory A could become refuted without theory B becoming necessarily refuted as well. I imagine: Some yet undiscovered effect is observed which is incompatible with theory A, maybe it leads to a contradiction. But for theory B it’s nothing more than a yet unexplained phenomen - B just can’t provide the explanation for it, because it is incomplete, like most theories. Alternative scenario: The postulates of theory A turns out to be false, but not the postulates of theory B. The reason why I’m asking this question is because I was unable to make much sense of some answers I received to a question elsewhere in the forum. (The answers appeared to me to indicate that my above ideas about physical theories are not true.) So where’s the error ?