Why is "ф" used almost exclusively in loan words?

Question

It is a common bit of trivia that the letter Ф is an extremely reliable indicator that you are looking at a loan word. Wikipedia tries its best at mentioning a couple of words of Slavic origin, but they are few and far between:

В современном русском языке буква «Ф» используется почти исключительно в заимствованиях, обозначает глухой твёрдый звук [ф] или мягкий [ф'] (перед «е», «ё», «и», «ю», «я» и «ь»). В словах славянского происхождения «Ф» встречается в звукоподражаниях (фукать, фыркать) или в словах, сильно изменивших свою звуковую и письменную форму (филин, Фили).

My question is: why is that the case? Certainly /f/ an extremely common sound in Russian. It is an integral part of the Russian phonological grammar — and in fact, there'd be no reason to introduce a dedicated letter for a sound that is not. It'd be rather silly indeed. I struggle to think of anything remotely similar in other languages.

So what's the deal here? Why is it that even after centuries have passed, and even after Ѳ has been discarded for good, Ф has still barely got any traction outside of loan words?

Answer 1

The reason why a special letter was introduced for a foreign sound is quite simple, the classical Cyrillic alphabet included all the letters of the Greek alphabet, including Ѳ and Ф.

In the modern Russian, [f] is not used almost exclusively in loan words, as you put it, it is used in numerous original Russian words and in different suffixes, only it is spelled like в, not like ф. Before a voiceless consonant the letter в is pronounced as [f] in words like завтра, вчера, второй, вперёд, etc. In the end of a word before a pause it is also [f], like in котов, зубов, узнав, дав, написав etc.

But the reason why /f/ was not a part of the Proto-Slavic inventory of phonemes has no possible answer, asking about it is like asking why Slavic languages lack interdentals, like the English /ð/, or emphatic consonants, like the Arabic /sˤ/.

Answer 2

A more correct question would be, why other Indo-European languages have /f/. This is because the Proto-Indo-European language had no such sound.

For example, in English word-initial /f/ evolved from PIE /p/, in Greek the evolution was from PIE /b^h/ via /p^h/.

Answer 3

Russian language have few own words with "Ф", because we prefer more strong sound "В". But in other countries F is one of most popular letter. Gradually this words going in our language and today we have more foreign words with "Ф" then own.