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.
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.
If T_{r} is the number of the
truth-grounds of the proposition "r",
T_{rs} 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
T_{rs} : T_{r}
the measure of the probability which
the proposition "r" gives to the proposition "s".