It is impossible to ever prove or disprove a theory, so falisfiability is a red herring. For a theory T and observations O, you can have 4 possible scenarios.

It is impossible to ever prove or disprove a theory, so falisfiability is a red herring. For a theory T and observations O, you can have 4 possible scenarios. Where "!" indicates "not": Starting from theory Modus Ponens : T therefore O Denying the Antecedant : !T therefore !O Starting from observation Affirming the Consequent: O therefore T Modus Tollens : !O therefore !T Denying the antecedent and affirming the consequent are both invalid if other theories may be consistent with the same observations (which is always the case), leaving us with Modus Ponens and Modus Tollens as valid forms of reasoning. What this means is that we can deduce: 1. what we should observe if our theory is really true (Modus Ponens) 2. a theory is not true if we fail to observe what it predicts (Modus Tollens) Modus Ponens reasoning is used to derive testable predictions from a theory, and then Modus Tollens reasoning is used when checking if the theory predicts the correct observations. However, the relationship between theory and prediction P is not so simple. It is always the case that other assumptions A must be made along with the theory. These assumptions can be as simple as "the equipment is functioning properly", but can get much more complicated.[1] I.e.: (T AND A) entails P If we fail to observe the prediction P, then the entire left side gets negated: !P entails !(T AND A) This is equivalent to saying either T or A is incorrect: !P entails !T OR !A So even in the best case scenario, you can never know if it is your theory that is wrong or some other assumption you making is wrong. This should tell us the real value of science lies somewhere else besides falsifiability, e.g. in making useful or otherwise surprising predictions. [1] https://en.wikipedia.org/wiki/Duhem%E2%80%93Quine_thesis https://en.wikipedia.org/wiki/Duhem%E2%80%93Quine_thesis