There are indeed valid methods, with hypotheses of a different nature, of the strictest nature, which requires that the actual cause be only one of the possible causes for itself, by those who gradually admit the denials, conjunctions and disjunctions of possible causes and combinations of these causes, to the least rigorous type of hypothesis that simply says that the real cause of these possible causes is constructed in one way or another. This reasoning illustrates Mill`s method of residues: many elements of a complex effect are demonstrated by reliable causal beliefs from several elements of a complex cause; All that remains of the effect must have been produced by the remnants of the cause. Note that if we accept the truth of all the relationships of cause, this method becomes an application of the deductive argument. Symbolically, the method of accompanying variation can be presented as (with ± represent a displacement): symbolically, the common method of concordance and difference can be presented as: as it will generally not be plausible to make the hypothesis stricter than a species (8), the conclusion thus established will only be that this individual sequence is an example of a flawed causal law. form (A… or…) is necessary and sufficient for P in F. But that is exactly what our ordinary claims of causality mean: to say that it only means that it was necessary, perhaps in conjunction with other factors that existed to produce the effect, and this openly leaves us that other precursors could produce the same effect overall (in this case non-existent). If two or more cases where the phenomenon occurs have only one circumstance in common, then two or more cases in which it does not occur have nothing in common, except the absence of that circumstance; the fact that the two groups stand out alone is the effect or cause or a necessary part of the cause of the phenomenon. It is important to remember that the use of the scientific method attempts to confirm or disprove a hypothesis; However, this process must always be considered partial and temporary. The weight we give to a confirmation or rebuttal is never all or nothing. We need to gather evidence over a long period of time. If we make mistakes, they are revealed by the results of repeated experiments. The corresponding variant (3.2) of the differential method requires only the observation of 1.2; but it merely finds the less complete conclusion that (A…) is a necessary and sufficient condition of P in F.

Indeed, while B, C, D and E singly are still eliminated (in the index for 1.2 above) as they were in 1.2, and that all conjunctions such as those that might be present in I1 are eliminated because they are also present in N1 and are therefore not sufficient, a conjunction like AB, which contains A, is present in I1. , and missing in N1, and can therefore be both necessary and sufficient. Thus, this hypothesis and observation only show that, as Mill said, A is «the cause or an indispensable part of it.» The full cause is represented by the formula (A…), provided that only the possible causes present in I1 can replace the points. One of the main characteristics of scientific methodology is verification and falsification.