多音字 – one of my favorite complications in learning Chinese. In another post, we have already dealt with 白讀 and 文讀 pairs like 白 [pai] / [puo] (from older [bak]), 色 [shai/se] (from older sek) etc. Today’s topic is another large group of 多音字: 去聲-derivatives. In other words, characters which can be read in two different tones, one of which is usually a 去聲, like for 教 or 要.
I am calling them derivatives because I assume that one of the readings is derived from the other in the same way that “to book” is derived from “a book” (more easily recognizable in German: Buch -> buchen), and that the 去聲 variant is usually the derived one.
Two questions suggest themselves: (1) how do I know and (2) why do I care?
As for question (1), I have observed that 多音字 come in three main types:
- 白/文 pairs, recognizable by their typical vocalism (mostly old 入聲 words)
- Same character, unrelated meanings (typically due to “simplification”, think 干)
- Two readings with related meanings but different tones – our topic today
For the last set, one of the two readings is usually a 去聲 , as in 王 king (P) and to be king (Q). Of course, I was not the first to notice that, see  for more on the topic. Given that the 去聲 is nowadays reconstructed as -s (and perhaps also -t) from comparative linguistics, the rule “QS = derived word” seems logically appealing. (Note: by rule I mean: for a 多音字; there are original QS words, like, well 去).
As for (2), why would I care? Well, I like to sort things into boxes. Rather than having to learn a bunch of unrelated phenomena, I would rather learn one general rule. E.g in English, if I know that to widen comes from wide, I have no trouble understanding loosen, strengthen, heighten – rather than one word, I have just learned a whole class. And I am hoping to do the same in Chinese.
Now, the example of “-en” derivations in English is a very fitting one, because (unfortunately) there is more than one “-en” class. There is the adj./noun => verb pattern we just discussed. But the same ending can also be used to make adjectives from nouns: gold-en, old-en, flax-en, earth-en, wood-en, wool-en … basically a whole host of materials can be turned into adjectives this way (but by far not all: there is no coal-en or steel-en). And then, of course, “-(e)n” is also used to form many past participles: risen, slain, sunken, seen, been. A quick analysis of English shows that there are at least 3 different classes of -n derivatives. So, is it even worth thinking about it? — I believe it is, because at the very least I now have three boxes that I can sort new word pairs into: they are either participles, adjectives formed from the names of materials or verbs made from nouns/adjectives by adding -en. Complicated, but better than complete randomness ;-).
So, on to find some new boxes in Chinese. Here is my working model (simplified for practical application from  and others):
(1) Noun => Q-verb
差: P: difference, Q: to differ from, to lack (P also be used as a verb “to differ”, see below)
釘: P: nail, Q: to nail
家: P: family, Q: to be given in marriage (written: 嫁)
王: P: king, Q: to be king
衣: P: cloth, Q: to wear
中: P: center, Q: hit the center
(2) Verb => Q-noun
藏: P: to conceal, Q: a storehouse
處: S: to be at, Q: place
擔: P: to carry/shoulder , Q: a load, a carrying pole
分: P: to divide, Q: part (cf. also 份; note: Q has voiced initial)
縫: P: to sow, Q: a seam
觀: P: to watch, Q: a watchtower, monastery
教: P: to teach, Q: teaching, religion (Qu-sheng also used for compound verbs, e.g. 教誨)
捲: S: to roll, Q: a scroll (卷)
空: P: to be empty, Q: spare time (also used for “to make empty” – see below)
量: P: to measure, Q: a measure, quantity (but also for “to assess” – one’s strength etc.)
磨: P: to rub, Q: a grindstone
難: P: to be difficult, Q: disaster
搧: P: to fan, Q: a fan (扇)
乘: P: to ride, Q: carriage
數: S: to count, Q: number
彈: P: to shoot, Q: a bullet
聞: P: to hear, Q: reputation
知: P: to know, Q: wisdom (智), wise 
傳: P: to transmit, Q: a record
Here one may argue for some words that the Q was the original, as the P or S has an additional 手 radical to distinguish the verb from the noun. Not necessarily, though – such radicals are often added by later generations “for clarification” and are missing in older text (think 捨/舎).
In any case, if you want to remember only one rule: “when in doubts, the noun is qù” covers the largest number of cases ;-).
(3a) Q-word with a “more restricted meaning”
差: P: to differ Q: to differ from, to lack
要: P: to demand, Q: to want
量: P: to measure, Q: to assess (also: “a measure”, see above)
少: S: to be few, Q: to be young
轉: S: to turn (trans.), Q: to revolve
(3b) Causatives (make somebody do something):
空: P: empty, Q: to empty
飲: S: to drink, Q: to give to drink
買: S: to buy, 賣 Q: to sell (note: character change)
散: S: be loose, Q: to scatter
But note 轉 as a counter-example above, where the qù-sheng is intransitive!
(4) Mixed bag of Qs
間: P: between, Q: gap, to separate
Of course, there are still pairs left which have nothing to do with 白/文 nor 去聲 derivatives, like 將, 沒, or 長. But classifying away a big part makes it easier to deal with the rest ;-).
 Guillaume Jacques. How many *-s suﬃxes in Old Chinese? . Bulletin of Chinese linguistics, Brill, 2016, 9 (2), pp.205-217
 Branner, D. (2002). Common Chinese and Early Chinese Morphology. Journal of the American Oriental Society, 122(4), 706-721. doi:10.2307/3217611
Additional examples from: http://news.sina.com.cn/o/2013-11-12/151928689420.shtml