> > The rationale was that this and certain other rules of English grammar are artifacts from Latin which don't necessarily belong in our own language. English isn't even a Romance language, yet because Latin was always stressed in the educational system, its grammatical rules were applied to English as well.
>
> Latin purists are attributed with the "no split infinitives" rule, too.

A third rule bequeathed to us by the Latin purists is the rule forbidding the use of "they" as third person singular.
Before the 18th century someone could merrily split their infinitives without anybody complaining their grammar was all stuffed up.
In the 18th century these rules were introduced by the aforesaid Latin purists, also known as Prescriptive Grammarians.

Pres( ;-} )Gram