Rhetorician Revised Version--RRV
Since Paul’s use of argumentum a minore ad maius in Romans 11 is a more complicated variation on the theme, we might do well to consider a much simpler example from Jesus’ teaching and then graduate to Paul. In Matthew 6, Jesus lays out the cure for anxiety:
”Look at the birds of the air, that they do not sow, nor reap nor gather into barns, and yet your Heavenly Father feeds them. Are you not worth much more than they? . . . And why are you worried about clothing? Observe how the lilies of the field grow: they do not toil nor do they spin, yet I say to you that not even Solomon in all his glory clothed himself like one of these. But if God so clothes the grass of the field, which is alive today and tomorrow is thrown into the furnace, will He not much more clothe you?” (vv.26-29 NASB Updated).
Jesus’ use of minore ad maius in this instance is straightforward:
Birds need to eat, and humans need to eat. If God provides food for the less valuable species (viz., birds), then will he not also provide food for the more valuable species (viz., his children)?
In other words, what is true on a smaller scale will be even truer on a larger scale, provided both scales include the same analogs (or points of comparison).
Another teaching of Jesus which involves the smaller-to-the-greater reasoning, except in a slightly more complicated way, occurred when the crowd that witnessed Jesus' healing of the man at the Pool of Bethesda on the Sabbath (see John 5:1 ff.) had the temerity to accuse Jesus of being demon possessed! Looking into their hearts, Jesus recognized the crowd's hatred of him and his methods. He knew they wanted to kill him.
Jesus then attempted to use reasoning as a way of getting his critics to see both the error in their ideology and his rightness in doing what he did. Jesus argued the following:
Moses and the fathers gave to the Jews the rite of circumcision in the Law.
The Law is actually from God, and the highest law is love, love for God and love for neighbor. The entire Law hinges on these two loves (see Deuteronomy 6:5 and Leviticus 19:18).
In fulfillment of the Law of Moses, male babies are circumcised on the eighth day after birth, even if that day happens to be the Sabbath. This "injuring" of the baby, though slight, makes him temporarily unwell; that is, until his wound heals.
I didn't injure a man; rather, I healed his entire body on the Sabbath. Why, then, are you criticizing me? If it's OK to injure a baby on the Sabbath so that the Law of Moses is not broken, how can you criticize me for demonstrating the higher law of love by not injuring a part of a baby but healing an entire man?
In other words, Jesus was asking the aggressive crowd, “If a baby's penis is cut in obedience to the Law, and that's OK, how can the healing of a man who has lived with an affliction for 38 years by an act of love, which is at the very heart of the Law,not be OK? That doesn't make any sense."
The reason I compare Jesus' thinking to Pauls' thinking in Romans 11 is that their reasoning is quite similar.
Jesus: If it's OK to inflict a small injury on a baby in deference to the Law of Moses, which is the lesser (and also a negative thing for the baby!), then why should it not be OK to perform a miracle of healing of a fully grown man on the Sabbath, which is the greater (and also a very positive thing for the man!?
Notice the similarities in Paul’s argument:
Paul: If the majority of the Jews transgressed, which is the negative and lesser thing, and their transgression led to the salvation of the Gentiles (i.e., the "world" at large), which is the positive and the greater thing, how much greater will be the restoration of Israel when the righteous remnant fulfills their God-given destiny and becomes a nation under God again.
As for Paul's argument and logic in Romans 11, they can be a bit slippery, and the moment you think you've got a handle on them, they slither right through your brain. (At least that's been my experience.) While his logic does not follow exactly the argumentum a minore ad maius format, there are certainly elements of that locution in the Gospels and in Romans 11.
Furthermore, the logic of "how much more" is certainly part and parcel of Paul's train of thought here. Some of the key words of his argument would include the words transgression, jealousy, fulfillment, and of course how much more.
Step By Step
A remnant is by nature "just a few." Paul is therefore contrasting the larger (i.e., "the world" of Gentiles) with the smaller (the remnant of a believing, Christian subculture within the larger culture of Judaism). Paul and a majority of Christ followers at that point in history were part of a remnant; namely, Jews who had believed on the Lord Jesus Christ as their Messiah.
The nation of Israel, on the other hand, had transgressed (vv.11-12), was hardened (v.7), and became that branch of the cultivated olive tree which was broken off (v.17 ff.), so as to allow the branch from the wild olive tree, the Gentiles, to be grafted in to the cultivated tree, Israel.
Consequently, Israel, with her former, favored nation status before God, was “put on hold,” so to speak, because she, as a small but proud nation, had become hardened spiritually. Her on-hold status, however, will one day, according to Paul, be lifted, and her ultimate destiny be fulfilled (v.13). John’s Revelation of Jesus Christ clarifies how Israel will once again in God’s economy loom large in world affairs and become once again one nation under God.
Now, if Israel’s transgression of unbelief and her subsequent hardening can make the Gentile world rich (which is clearly a wonderful thing, since God's forgiveness, grace, and mercy are bringing multitudes of believers into the family of God), how much more will her restoration enrich the entire family of God, both Jew and Gentile. Israel's temporary hardening surprised God not a whit. Furthermore, in his covenant with Abraham centuries before the Apostle Paul came on the scene, God told Abraham that through his seed, all the nations of the world would be blessed (see Genesis 12:3, and the repetition of the covenant to Jacob, Genesis 28:14).
This, then, is the essence of what Paul is saying in verse 12:
Something good came out of something bad. If at some time in the future, with the bad having become good once again, then logically the end result will be even more glorious. In other words, if Israel’s unbelief meant riches for the world at large, the fulfillment of her restoration to belief will mean even greater riches for the world and for Israel.
In conclusion, the argumentum minore ad maius figures prominently in Scripture, and I suppose an entire book could be written about its rhetorical uses in the pages of holy writ. Perhaps the OP could consider taking on such a project!?