Why use two scripts for the same language?

There are about fifty known monumental inscriptions in the two Khitan scripts, of which about 17 are in the Khitan Large script and about 33 are in the Khitan Small script, which suggests that the small script was more widely used than the large script, but it is not known why the Khitan people used these two different scripts, or what determined the choice of which script to use. Japanese uses multiple different scripts (kanji, hiragana and katakana), but these are differentiated functionally, and are normally used in conjunction within the same text; whereas the two Khitan scripts appear to be mutually exclusive as they never occur together on the same monument or artefact. Why then are there two Khitan scripts ?

Hypothesis A : Chronological Variation
The first idea that springs to mind is the possibility that the two scripts were not used at the same time. Perhaps one script was used first, but was later displaced by the other script. The Khitan Large script was created in 920 at the request of the Emperor Taizu, and the Khitan Small script was created about five years later. We might therefore expect that the large script was used during the reign of Emperor Taizu, and the phonetic small script gradually become more widely used after the death of the emperor in 926, eventually displacing the more cumbersome large script. However, this is not borne out by the extant corpus of inscriptions, which show both scripts co-existing happily for at least 200 years. It was only with the proscription of Khitan by the Jurchen court in 1191–1192 that both scripts finally fell out of use.
Hypothesis B : Geographic Variation
If the Khitan scripts do not show any significant chronological variation, then perhaps they show a different geographical distribution, with the small script used in one part of the Khitan territory, and the large script in another part of the Khitan territory. But this does not appear to be supported by the distribution of inscriptions (see the map at Blog from WayBack Machine). Although there does seem to be some clustering of Small script inscriptions, there is no obvious geographical distinction between the two scripts.
Hypothesis C : Different Functional Usage
Perhaps the two scripts had different functions, for example one for writing religious texts and one for writing secular texts, or one for writing official and court documents and one for writing private and personal documents ? But as both scripts were commonly used for exactly the same function (writing memorials for the dead) this theory seems to be a non-starter.
Hypothesis D : Different Social Usage
Maybe the two different scripts were used by two different sections of the Khitan population. Was one script used by men and the other script used by women ? This seems not to be the case, as both scripts are used to write memorials for both men and women. Was one script used by royalty and nobility, and the other script used by commoners ? Probably not, as there are memorials to princes and princesses in both scripts, although the only memorials to emperors and empresses found so far are in the small script. Were the scripts used by different clans ? Again, there is no evidence for this, as both scripts were used to write memorials for members of the Yelü 耶律 clan.
Hypothesis E : Different Linguistic Usage
A final possibility is that the two scripts were used to write two different languages or dialects. Although there is no evidence that the Khitans spoke more than a single language, it is a possibility that cannot be discounted. But it is a theory that is difficult to prove or disprove as most of the Khitan words that have been identified in the small script are borrowings from Chinese, and almost all the large Khitan script words for which a reading has been proposed are also borrowings from Chinese.

Having looked at and discounted the various possibilities outlined above, we seem to be none the wiser about why there were two completely different ways of writing the Kitan language. Both scripts are complex enough to require a considerable investment of time and effort to learn to read and write, so it remains a mystery how and why both scripts managed to coexist and flourish for so long.

Reference: What’s the Difference, Andrew West, 2010. Blog (WayBackMachine)

This article formerly appeared on ScriptSource.