This notion is given in clearer terms by Jevons and Creighton. Viz.: “The sole invariable antecedent of a phenomenon is probably its cause”; and “The sole invariable consequent of a phenomenon is probably its effect.”
It is known that an antecedent is anything which precedes; while a consequent is anything which follows. To be regarded as a cause, an antecedent must be invariable, and to be regarded as an effect, a consequent must likewise be invariable. Antecedents and consequents which are in no way constant could hardly have any causal connection.
(2) Method symbolized. Let P₁, P₂, P₃, P₄, etc., represent the phenomenon as it may appear the first, second, third, fourth, etc., times, and let A, B, C, etc., stand for the various antecedents, or the various consequents as the case may demand. These two forms may now be used to illustrate the two statements which summarize Agreement:
First statement.
Antecedents. Consequents.
A B C D — P₁
A D E F — P₂
A L M N — P₃
A O P Q — P₄
Second statement.