# Short ‘i’ in Fīō

As I discussed in the last post, certain forms of fīō feature a short i instead of the usual long. I thought there would be a long and complicated phonological history to tell, but it turns out fīō is just following a few phonological rules that we already know.

Long vowels before final m, r and t are shortened.

• amō, amās, amat
• amem, amēs, amet
• amer, amēris, amētur
• so also fīō, fīs, fit

The second rule is more exclusive to fīō, but follows a consistent pattern: the ī is shortened before -er.

• fierem, fierēs, fieret; fierī

The Essential AG: 603.3, 606.3a