AA / AABB

Doubling an adjective makes the description vivid – a picture of how something looks or feels, with a little more intensity than the plain adjective. A one-syllable adjective doubles straight; a two-syllable one doubles each half.

The two shapes

One syllable: 大 → 大大, 高 → 高高, 慢 → 慢慢. Two syllables split and double each half: 干净 → 干干净净, 高兴 → 高高兴兴, 漂亮 → 漂漂亮亮.

• × 干净干净 → 干干净净

As a manner adverb

With 地, the doubled form describes how something is done. This is where you meet it most.

In speech the 地 is often dropped: 慢慢说. hǎo hǎo好好 before a verb means "properly" or "thoroughly": 好好休息, 好好学习.

的 after the doubled form

Before a noun, and at the end of a sentence, the doubled form takes 的.

No degree adverb

The doubled form already carries its own degree, so 很, 非常 and 太 cannot go in front of it, and neither can 不.

• × 很大大的 → 大大的
• × 非常干干净净 → 干干净净