my unproven pet Theory is that Sanskrit still had the F sound but it was lost and re-interpreted as “i”: पि This theory is motivated by the observation that w

my unproven pet Theory is that Sanskrit still had the F sound but it was lost and re-interpreted as “i”: पि This theory is motivated by the observation that words with पि have an ( inclination towards) F in other branches of Indo-European (Also just the left-hand side of पि without the 'P' which cannot be pasted due to Unicode restrictions) Eg https://en.m.wiktionary.org/wiki/पितृ#Sanskrit https://en.m.wiktionary.org/wiki/पितृ#Sanskrit fpita’=father fp Here could have been a merged consonant, similar to PF in German: But in other cases just a pure F