The method of agreement is then highlighted as a cause of a common characteristic in a number of otherwise different cases where the effect occurs; the difference method takes as its cause the only thing in which a case where the effect occurs differs from an otherwise exactly similar case in which the effect does not occur. Both are supposed to be methods of amplifying induction, i.e. methods that allow us to obtain a general cause-and-effect link from a limited number of observed cases: the expected conclusion is that a particular disease is always produced by a lack of fresh fruits and vegetables, or that the immersion of iron in water, while it is hot, always hardens it. if it has been heated and hammered in some way. And the other three methods must work in the same way. However, where we have a very large number of extremely different cases of effect and there seems to be only one factor in all of them, we can use a 8.12 method actually closer. The various proceedings cover at least a wide range of all possible combinations of potentially relevant factors and their negations. Therefore, it is likely that no condition that is not covered by the formula (A or…) is necessary, and therefore, if there is a necessary and sufficient condition, (A or … ) is so, and therefore A itself is a sufficient condition of the phenomenon. The common method can be interpreted as an indirect method of difference, i.e. the task performed by I1 above can be divided between several positive instances and the work done by N1 between several negative instances.

This means that we need (for 1.3) the following observation: an amount of if one or more positive instances and a Sn amount from one or more negative instances, so that one of the possible causes, for example. B A, is present in all Si and lacks in any Sn, but each of the other possible causes is absent either in at least one positive case or in at least one negative case. Given that one of the possible causes is both necessary and sufficient, the conclusion is that this is the case. The most important authors who have tried to develop Mill`s ideas on the logical side are W. E. Johnson, Logic (Cambridge, U.K., 1924), Part II, Ch.