Functional Directions "Up" and "Down"
Many directions are functional, that is, words such as "up" and "down," "right" and "left" that help us teach and understand specific characteristics of Chinese culture.
shàng 上 ascending, previous xià下 below, lower, next
Word "parallels" exist in functional directions to express conditions unique to that language. One good example of this is the pair shàng 上 ascending, previous and xià 下 below, lower, next.
上课 shàngkè means to attend class, or to give a class 下课 xiàkè means to finish class, to dismiss. 上班 shàngbān means to start work, and also to be on duty, start work 下班 xiàbān off duty, leave work. A wide variety of parallel actions are expressed: shànglái 上来 come up xiàlái 下来 come down, get off
The day is also divided by this parallel construction.
上午 shàngwū is the late morning, basically 9 or 10 am to noon. xiàwū下午 is the early afternoon, 1 or 2 pm until 5 pm.