Why is There a Spelling Shift in the Stem of Verb "reperire"?

Question

Verb, "reperio" [4]--"find", "find out"; "discover"; "invent" (Oxford) has these principal parts: "reperio", reperire, repperi, repertum. Note that the third part, the past perfect, has the letter 'p' twice, in the stem; the other parts, one 'p' only, in the stem.

Here's an example of the past perfect from the Wiki entry:

"occasionem repperisti, verbero ubi perconteris me, insidiis hostilibus,"--

"You have found an opportunity, scoundrel, when you question me amid hostile ambush," (Plautus, Pseudolus 4.4.9-10)

Is there a logical reason for this spelling shift or is it a quirk of linguistic evolution?

Answer 1

It's due to reduplication in the original stem. One way the perfect was created in PIE was by reduplication of the first syllable. For pario, note that the 1st person singular perfect is peperi, similar to the Faliscan pe:para[i] (De Vaan).

When re- prefix was added, the accent shifted to the first vowel (as it did in older Latin), which led to that reduplicated "e" being weakened and eventually lost in Latin. You thus end up going from *repeperi to repperi.