The truth-functions can be ordered in series.
That is the foundation of the theory of probability.
5.11 If the truth-grounds which are common to a number of propositions are all also truth-grounds of some one proposition, we say that the truth of this proposition follows from the truth of those propositions.
5.12 (4) In particular the truth of a proposition "p" follows from that of a proposition "q", if all the truth-grounds of the second are truth-grounds of the first.
5.13 (6) That the truth of one proposition follows from the truth of other propositions, we perceive from the structure of the propositions.
5.14 (3) If a proposition follows from another, then the latter says more than the former, the former less than the latter.
5.15 (6) If Vr is the number of the truth-grounds of the proposition "r", Vrs the number of those truth-grounds of the proposition "s" which are at the same time truth-grounds of "r", then we call the ratio Vrs : Vr the measure of the probability which the proposition "r" gives to the proposition "s".