Reconstructing Old Chinese
The spelling of words is often an indication of how they used to be pronounced. A quick look at French spelling tells us that the modern language must have lost a lot of final consonants. English spelling also tells us that some words such as “love” and “move” used to rhyme but now don’t.
But with a character based system the job of figuring out what the Chinese language used to sound like must be a lot more difficult. So how do linguists do it?
One way is to look at pronunciation in other languages. Chinese cultural influence in East Asia is huge, and so there are lots of loan words that made their way from Chinese to other languages such as Korean, Vietnamese and Japanese. Since many loan words were adopted hundreds of years ago it is possible to look at the pronunciation of loan words in these languages to get an idea of what the Chinese pronunciation was when they were first introduced. For example, the Japanese word for “problem” is pronounced もんだい (mondai) which is a lot closer to the Cantonese pronunciation (man6 tai4) than it is to the Mandarin (wèntí). This doesn’t do too much to tell us what Chinese used to sound like, but it at least helps determine which present day Chinese dialects are more conservative and thus more likely to be closer to how Chinese sounded in the past.
For more specific reconstruction of what Chinese used to sound like, linguists have used several historical documents or “rhyme dictionaries” that record Chinese pronunciation. One of the most famous is the guǎng yùn rhyme dictionary that was completed in 1011AD, during the Song dynasty. As the name suggests, these documents group characters together on the basis of whether or not they rhyme. They used a system called fǎn qiè in which the pronunciation of a character is represented by two or three different characters. Since all Chinese characters are one syllable long, the two or three characters would represent the first second and third sounds in the syllable. Basically, if you wanted to represent a character with the pronunciation “mei” you would use two different characters; one that begins with “m” and one that ends with “ei”, a bit like this:
美 = 慢 + 给
měi = m(àn) + (g)ěi
Some of these rhyme dictionaries from the Song dynasty also categorised characters on the basis of tone, consonant initial and consonant final. Although there is no way of knowing what the exact tonal values were, linguists at least know how many tones there were and the most likely directions of those tones. Similarly, Chinese linguists at the time had ways of describing consonant sounds based on the points of articulation, and these descriptions are written into the rhyme dictionaries. For example, chún 唇 referred to labials (consonant sounds made with the lips) and chǐ 齿referred to dentals (sounds made with the teeth). It’s nowhere near as detailed as the international phonetic alphabet used by linguists today but it’s a start. All this information can then be compared to the present day dialects and the loan words into other languages that most closely match these descriptions to get an idea of what Chinese used to sound like.