To close the list, that is to say to show that certain factors are irrelevant, we must use an analog of the method of agreement. If we assume, as is the case so far, that the complete cause of P to F is a few factors (X, X, X”, etc.), but also that P reacts to all these factors in the sense that for each variation, in, say, X, X, etc. remain constant, p varies, and that X, X, X, X etc. are identical to some of the possible causes A , B, C, D, E, if we discover that P remains constant, while. B, for example, A, C, D and E remain constant, but B varies, we can conclude that B is irrelevant, that none of the X is identical to B. When we assume the second type (whether the required condition is either a possible cause or a negation of a possible cause), we need stronger observations. For variants of the positive method of the Agreement (2.11 and 2.12), we therefore need this: two or more positive instances, so that in all cases there is a possible cause (or negation), for example. B A, but for any other possible cause, there is a proceeding in which she is present and a proceeding from which she is absent. This is necessary to exclude as a candidate for the role of the necessary (or necessary and sufficient) condition, the denial of possible causes as well as possible causes other than A himself. On the other hand, the difference method (4.2) requires only the observation of 1.2; This eliminates all possible causes, except A and all disjutions that do not contain A, either as insufficient because they are present in N1, or because they are not necessary because they are missing in I1. The only ones that are not eliminated are those that appear in I1, but not in N1, and these must contain A. Thus, this observation shows with this hypothesis that a necessary and sufficient condition (A or…) is, i.e.
either A itself, or a disjunction containing A, where the other disjunct causes are possible causes that are lacking in N1. This, of course, means that A himself, the factor thus chosen, can only be a sufficient condition for P. The common method as an indirect method of difference no longer works as soon as we allow both conjunctions and disjunctions; but a dual method of agreement comes into force with this eighth type of acceptance. In 8.12, as in 6.12, if there are possible causes except A, the set of 2n positive instances with A that are present in each, but with the other possible causes present and absent in all possible combinations, show that (A or…) is necessary and sufficient, and therefore that A is sufficient.