Reasons for Chinese changing from monosyllabic to disyllabic?

Question

Classical and Middle Chinese are often considered monosyllabic languages - most words are single syllables. Modern Chinese however is considered disyllabic - most words are two syllables.

For example, take this excerpt about the Battle of Red Cliffs, from Records of the Three Kingdoms, a text written in the 3rd century, in Classical Chinese:

公至赤壁，與備戰，不利。 (Cao Cao came to Red Cliffs, fought with Liu Bei, and lost.)

If that passage were to be written in modern Chinese, a lot of words might become disyllabic. For example, 公 = 曹操, 至 = 到达, 備 = 劉備, 戰 = 作戰 and so forth.

My question is what are the main reasons for this transition?

Answer 1

The Phonology of Standard Chinese by San Duanmu (端木三) has an entire chapter devoted to this topic (The Word Length Problem):

In this section I review six previous approaches to the disyllabic phenomenon in Chinese. For convenience, I call them (a) the homophone-avoidance approach, (b) the speech-tempo approach, (c) the grammatical approach, (d) the rhythm approach, (e) the morphologization approach, and (f) the stress-length approach. These approaches are not all proposed by different people. For example, Guo (1938) suggests that both (a) and (b) play a role, Lü (1963) suggests that both (b) and (c) play a role, and N. Li (1990) suggests that both (c) and (d) play a role. I argue that none of the approaches, nor combinations of them, can explain the disyllabic facts adequately.

In my own readings, I found that the homophone-avoidance approach (which @user58955 explained in his first point) to be the most common explanation. It feels true too because phonological changes since Old Chinese have merged the pronunciation of many words that were once distinct, and modern Chinese languages that have been more phonologically conservative tend to retain more monosyllabicity (such as Min and Cantonese). The book points out several issues with the homophone-avoidance explanation though:

...as Lü (1963) points out, most increase in disyllabic words took place in the past 100 years or so, during which period there has been little change in the phonology of Chinese.

However, this objection could be partially explained by the rapid incorporation of modern concepts (which @user58955 explained in his second point).

There is another interesting point concerning the homophone-avoidance approach:

... many proponents of homophone-avoidance ... assume that classical Chinese mostly consisted of monosyllabic words. However, when Chinese characters were created ... Chinese already had numerous homophones. ... In other words, there must have been many homophones from the beginning. This raises the question of why people did not create disyllabic words to avoid ambiguity then. The answer, as suggested by Guo (1938), must be that classical written texts did not reflect the spoken language, in part because of the scarcity of writing materials, and in part because characters offer more distinctions than speech. ... In any case, there is no clear evidence that classical spoken Chinese mostly consisted of monosyllabic words.

Anyway, the chapter is an interesting read. The conclusion eventually states:

I have also argued that, unlike a popular belief, homophone-avoidance does not play a clear role in the increase of disyllabic words in Chinese. Instead, the increase is mainly due to an increase in new words...

Finally, I have argued that word lengths are constrained by metrical structure, in that some positions prefer a disyllabic words and other prefer a monosyllabic word. ...

Answer 2

1. The pronunciation is getting simplified (for some unknown reason) and the number of homophones has increased a lot. In order to avoid the ambiguity, it is natural to encode more information (using additional characters).

   In some southern dialects, the old monosyllabic words are still in use. For instance, in Min dialect, 筷子 are still called 箸, 剪刀 called 铰, 悲痛 called 恻.

2. Concepts and notions are getting more and more complicated, which also demand more information to be encoded. Especially most modern concepts are introduced from the western world, and new words have to be created for those new concepts. A single character could be very inaccurate, so two or more characters are used.

   When the word like community or society or whatever was first translated into Chinese, the translator used the word 群, but then distinguishing among community / society / cluster / group becomes a problem, because they can all be called 群.

Answer 3

It is baffling to me why anyone could have ever have questioned the proposition that written Chinese DID NOT represented a monosyllabic, spoken language. The earliest examples we have represent a communication system with the spiritual world. The writers knew what they wanted to say, could the spirits not understand this shorthand approach? Of course they could! Even with four or more "tones," there is no way the human mind would ever have been able to understand the huge number of words any natural human language possesses...in the several tens of thousands at least. This idea that natural human language, used as a practical means of communication, could consist of 30~40~80,000 monosyllabic "words" is, to put it mildly, absurd. The evolution from a mono-character/syllabic system to what has become the modern norm of mostly di-syllabic words, can only be understood as moving from a communication system between human beings and the spirit world used for extremely limited purposes to one that gradually became a system used between educated human beings, again for less limited but just the same specialized purposes, and finally a communication system among all speakers of the language for all purposes. That is why the documents that we read throughout the centuries show a gradual movement from monosyllabic phrases that turn into di-syllabic words where one syllable modifies another, limiting the reference field of that syllable, making it more specific so that ordinary human beings, not gods, can understand what is going on. Another glaring error of the monosyllabic idea, as it particularly refers to a written language, is the appearance of "vernacular" novels during centuries when "Classical Chinese" was still be used for official and scholarly purposes. These novels, it can be readily and logically assumed, DO, represent the spoken language, and indeed can be read fairly well today....easier than Shakespeare, to be sure, for English speakers. It is also interesting to note that until the early decades of the previous century, "Classical Chinese" novels were also published for the "erudite" class who felt the vernacular written language was an abomination, an affront to their educational training by the uneducated. When I first read Norman's book I was no longer teaching but actually using Chinese every day as well as translating Classical Chinese. In the intervening years perhaps people in the academic field have debunked this monosyllabic theory...I hope so. It is so wrong-hedaded that one is at a loss to understand how the idea could ever occur to anyone. ##

Answer 4

It is just the difference between formal and informal, not about age. And actually, in most official document, you can still see many monosyllabic words, especially in countries using Traditional Chinese.