The verb agreement for "one" when used as a subject

The first sentence in "Blake" in The Sacred Wood by T. S. Eliot is

If one follow Blake’s mind through the several stages of his poetic development it is impossible to regard him as a naïf, a wild man, a wild pet for the supercultivated.

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Why did he use "follow", but not "follows"? Because this book has been reprinted for several times, the usage of "follow" here is not likely to be a typo.

EDIT: In Selected Essays, 1917-1932, Eliot changed "follow" to "follows".

Solution 1:

I believe this to be a pedantic application of the subjunctive mood following if.

If in the quote introduces something which Eliot
- wants to happen
- hopes will happen or
- imagines happening
and Eliot has used the subjunctive form of follow.