discussing God's punishment of Miriam by leprosy states
And the Lord said to Moses, If her father had but spit in her face, should she not be ashamed seven days? Let her be shut out from the camp seven days, and after that let her be received in again.
Rashi comments: We could equally argue that If her father embarassed her she would be
embarassed 7 days; hence if God embarasses her she should be shut out from the camp 14 days.
But we suffice with the analogy hence, when God embarasses her she should be shut
out from the camp 7 days. In other words, the driving force of the verse's logic is analogy-
father:7 days:: God:7 days. The Bible does not however use a fortiori arguments to intensify
(14 vs 7).
In this case Rashi is commenting on the logical inference in the verse. Hence we classify
this as a logical non-verse method similar to the numerical spreadsheet methods
and the diagramatic geometric methods.
We should also point out that very often
the validity and content of Biblical exegetical methods are
derived from verses. Here the method of application of the
a-fortiori argument is derived from a Biblical verse. Thus
these rules were not oral traditions from Sinai but
rather actual derivations from the Biblical text (and consequently
have Sinaitic force and authority.)