The student must regard the given illustrative symbolizations and concrete examples as being of the simplest form; in life such are the exceptions rather than the rule. When investigating questions, like the cause ofthe high cost of living, the effect of high tariff, the reason for the typhoid epidemic, etc., there is often a confusion of circumstances which makes the Joint Method unsatisfactory, even though it furnishes a larger opportunity for the multiplication of instances.
The strongest case which the Joint Method is able to present is when the negative instances repeat the positive in every detail, with the one exception of the variable antecedent. To wit:
| Strong Argument: | ||
| Circumstances | Phenomenon | |
| A B C | P₁ | |
| A L M | P₂ | |
| – L M | — | |
| – B C | — | |
| Weak Argument: | ||
| A B C | P₁ | |
| A L M | P₂ | |
| – R S | — | |
| – T K | — | |
Despite the disadvantages, the conditions of the Joint Method are more or less ideal; since the positive branch of the argument suggests the hypothesis, while the negative branch proves the accuracy or inaccuracy of such.
5. METHOD OF CONCOMITANT VARIATIONS.
(1) Principle stated.
Mill’s statement is this: “Whatever phenomenon varies in any manner whenever another phenomenon varies in a particular manner, is either a cause or an effect of that phenomenon, or is connected with it through some fact of causation.”
To put it differently: If when one phenomenon varies alone, another also varies alone, the one is either the cause or the effect of the other.
(2) Concomitant Variations symbolized.
| Circumstances | Phenomenon |
| A | P |
| A + a | P + p |
| (A + a) − a | (P + p) − p |