Pronunciation of 上下

Question

上下 has lots of potential pronunciations:

1. じょうげ
2. うえした
3. しょうか
4. かみしも

Are there any guidelines on how to know which readings to use? I'm particularly interested in this sentence:

顔が上下に割れるかと思ったほど大きくにっこりして、...
The person grinned so hard that he thought his face might split from top to bottom.

But I'd also be interested in more general thoughts.

Answer 1

As for your example, both じょうげ and うえした will work and I don't think I can choose one.

The first reading じょうげ is the most versatile one that spans across a number of related meanings as well as grammar:

1. n. top and bottom, upper and lower, the former and the latter (volumes), inbound and outbound (traffic); (adverbially) above and below
2. n. all from top to bottom, high and low
3. n. the quality of up and down, verticality, height, tallness, hierarchy, rank; (adjectively) vertical, hierarchical
4. v. move up and down, fluctuate, bounce; n. fluctuation, bouncing

うえした and かみしも each shares a small portion of the definition #1 (and #3) shown above. You can refer to Ups and downs: かみ・しも vs うえ・した for their difference, but simply put, うえした is used for something really "vertical", and かみしも specially for those customarily assigned "up" and "down" and not very "vertical".

• うえした: for physical position, dimension, direction and hierarchy
• かみしも: for river (up- and downstream), stage ("upper" (=left) and "lower" (=right)), kimono (top and bottom pieces), tanka etc.

But うえした has one unique sense not in じょうげ: "upside down" by its own (= 上下（じょうげ・うえした）逆). The similar usage can also be seen in native words 前後ろ, 裏表, 右左 etc.

しょうか is... never used anymore, except that since it is all-漢音 reading, it must (prescriptively) be used instead of じょうげ whenever we read Classical Chinese. For other meanings kindly consult the dictionary, because they are foreign to us too :)

故【ゆえ】に上下【しょうか】能【よ】く相【あい】親【した】しむなり。
Hence, as the superior and inferior, they are able to have an affection for each other. (James Legge)