Reading Moulton’s Prolegomena is always interesting. He was definitely a descriptive linguist and regularly comments on how English forms a given meaning both in terms of traditional grammar as well as what “the man on the street” would say.
Here are his comments on the English comparative forms for the adjective:
English affords us instructive parallels. The simplicity and convenience of our suffixes -er and -est have helped to preserve in common speech the old degrees of comparison. But how often does the man in the street say “the better of the two”? One would not like to say offhand how far in this matter modern literature is impeccable on Lindley Murray rules; but in conversation the most correct of us may at times be caught tripping, and even when the comparative is used we are most of us conscious of a kind of pedantic accuracy. That “the best of the two” is the English of the future is a fairly safe assertion. Whether, adjectivally, is as archaic as πότερος: when we translate τίνα ἀπὸ τῶν δύο (Mt 27:21) by the archaism “whether of the twain,” we are only advertising the fact that the original was normal speech and our translation artificial. We have not yet arrived at “either of the three,” but people say “either A. or B. or C.” without a qualm.
I find it interesting that expresses that were apparently becoming awkward sounding have done the exact opposite of Moulton’s prediction. “The better of the two” has definitely strengthened it hold (at least in North America) and “the best of the two” sounds okay to me, but somewhat stilted. And then expressions that I can only guess were natural in 1908, “the most correct of us,” and, “we are most of us conscious,” sound terrible strange to my ears.
Ah…language change. It’s so fascinating.