A Fortiori
An a fortiori argument is one “from the
lesser to the greater.” It occurs in Scripture. The author to the Hebrews
argues, for example, that if the Old Testament law was binding and
transgressions against it punished, then certainly (an implicit “all the more”)
rebellion against the New Covenant will be punished (Heb 2:3f.; Rom. 5:15, “For
if the many died by the trespass of the one man, how much more did God’s grace
and the gift that came by the grace of the one man, Jesus Christ, overflow to
the many!” cf. v. 17). One hears this type of argument also in theology. For
example, “If children received the sign of the covenant in the Old Testament, is
it not all the more likely that they would receive it in the New Testament as a
result of the greater grace of the New Covenant?”
Obviously, however, not all a fortiori arguments
are sound. Consider this one. “Since the poor are entitled to free medical
care, certainly the rich ought to be given the same.” Or consider this one. “If
God worked miracles prior to the closing of the canon, certainly He should do
so even more afterwards to testify to the completion of His revelatory work.”
And here is another: “If getting baptized once is a means of grace, getting
baptized many times is an even greater means of grace.” You can see that this
type of argument is not always cogent.
To avoid the pitfalls of a fortiori
arguments, we need to remember the following. (A) “Greatness” can mean
different things that presupposes different kinds of value judgments. (B) To
make an a fortiori argument work, the greatness must be of a type that
is relevant to the particular argument. (C) Even relevant forms of greatness do
not justify corresponding increases in all other variables. “Getting baptized
many times” is numerically greater than “getting baptized once,” but the former
is not accompanied by an increase of grace parallel to its numerical
superiority. (John M. Frame, The Doctrine of the Knowledge of God [A
Theology of Lordship; Phillipsburg, N.J.: Presbyterian and Reformed, 1987], 276-77)