I’m not sure when Sara Goldman asked me this question. I hope I answered her but I just found this blog entry that I had started but never finished. In case others might be interested in the origin of the distinction between soft Cs and hard Cs, will finish it now.
This is what Sara asked:
“When did the letter C change from the K sound to a soft C? I studied Latin; Caesar was pronounced [kaisar] from which comes German Kaiser, which means that’s how the ancient Germans pronounced it, I think. When I took Latin, all C’s were spoken K, e.g. circus was pronounced [kirkus]. But I’d like to know more about the K to C sounds.“
First, let’s talk about both [k] and [g] sounds since they are identical except you vibrate the vocal cords in your larynx when pronouncing [g]. Otherwise, both are pronounced by raising the tongue to the top of the soft palate way in the back of your mouth and momentarily stopping the flow of air from your lungs (try a few ‘kahs’ and ‘gahs’ and see for yourself).
Both these sounds tend to undergo “palatalization”, that is, their pronuncation changes because, over time, speakers move their tongues forward to the hard palate, where [ch] and [j] are pronounced.
This normally occurs when [k] or [g] are followed by a “front” vowel, a vowel formed by raising the tongue in the front of the mouth. Front vowels are [i] “ee” and [e] “ay” in most Indo-European languages. This is why soft Cs most often appear before I and E: city, certain but cough, catch.
The problem here, as you can see, is that a consonant, formed by raising the tongue to the back of the mouth, is followed by a vowel formed by raising the tongue in the front of the mouth. The tongue has to move a great distance in a very, very, very short time. The tendency is for the back consonants, [k] and [g] to move forward over time toward the middle of the mouth, where, as I mentioned, [ch] and [j] are pronounced.
These consonants usually spend some time as [ch] and [j], pronounced by raising the tongue to the middle of the mouth. This is why kirke became church everywhere in English except in Scotland, where you still hear kirk. (This is an example of the front vowel moving to the back to meet the consonant, too.) It is a common change, still rampant in Portuguese but common in Late Latin, just before it divided into French, Italian, Spanish, and Portuguese.
In French and Spanish, however, the [ch] and [j] sounds continued to move forward until they become [s] and [z], respectively, pronounced almost in the same spot as [ee] (letter I) and [e] (letter E). So what began as a [k] sound in Caesar [kaisar] became Cesare ([chesare]) in Italian, then moved on to become Caesar [sezer] in French and [seezur] when English borrowed it.
You can read about these changes in almost any history of Romance languages (whence we borrowed most of our words). My favorite is Martin Harris’s “History of Romance Languages” but you can find it along with Peter Boyd-Bowman’s “From Latin to Romance in Sound Charts” in most college libraries or at Amazon.com. (You can also find my The 100 Funniest Words in English there, too.)