忽 A 忽 B
now A, now B: switching suddenly back and forth
Structure
忽 单音节词 A 忽 单音节词 B（多为反义词）
What it means
“Now A, now B”: unpredictable switching back and forth between two states. 忽 is short for 忽然.
How it is built
忽 + one-syllable A + 忽 + one-syllable B, usually opposites: 这几天气温忽高忽低 (temperatures have been up and down). Others: 忽冷忽热, 忽明忽暗, 忽快忽慢, 忽隐忽现.
When to use it
Written and vivid. 忽冷忽热 can also describe a person who blows hot and cold. With two-syllable words use 忽而…忽而… or, in speech, 一会儿…一会儿….
Watch out
One syllable per slot: ✗忽高兴忽难过 ✓一会儿高兴，一会儿难过. It means repeated switching, not a single change.
Examples
醒来以后，他忽笑忽叫，拍着手冲出门去。
When he came round he laughed and shouted by turns, and rushed out of the door clapping.
这几天气温忽高忽低，很多人都感冒了。
Temperatures have been up and down these last few days, and lots of people have caught colds.
油灯的火苗忽明忽暗，照着他伸出来的两个指头。
The flame of the oil lamp flickered, lighting the two fingers he held out.
Learn this in Lesson 251 · HSK 9+: 《儒林外史》 (The Scholars)
A dialogue, a reading, word cards with audio and a drill that uses it, in Learn Chinese with Bao. The first lessons of every level are free.
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