subjunctive perfect vowel lengths

[Fredericus]

I'm all the way to Moreland & Fleischer's Unit 2 (whoo-hoo!), and have noticed a discrepancy in its Subjunctive Perfect Active forms and those of another couple of books I'm consulting (e.g., an old Jenney, I believe). M&H don't have macrons on the initial -i of the suffixes:

-erim
-eris
-erit
-erimus
-eritis
-erint

Whereas other books say the initial i is long, and so show macrons for -eris, -erimus, and -eritis. Without the macrons most of these forms collide with those of the Future Perfect Indicative Active.

Is this a change between an earlier form and a latter classical form, or different scholarly opinions on what the vowel length should be, North Latin and South Latin, or what?

[Ulpianus]

Both forms can be found (i.e. both long and short i). A+G suggest that the original form was long-i, but that short i became common precisely because of assimilation to the fut. perf.

Grammars seem to vary: some mark the i long, some leave it short, and some mark it as being either long or short.

[Fredericus]

Thanks; I'll just be on the look-out for both forms, then.

[Episcopus]

It's much like the varying short/long mihi/mihí (or even mí) which adds to the flexbility of lengths in writing poetry. I've seen both forms, but more of the short.