冇...咁

This pattern is the colloquial equivalent of the English 'not as... as'.

1. The Role of 咁 (gam3)
The word 咁 (gam3) is often used in this pattern to mean 'so' or 'that much', but it is not strictly mandatory. You can naturally omit it (e.g., 我冇佢高 ngo5 mou5 keoi5 gou1), though including it adds a nice emphasis to the comparison. When used, the adjective or stative verb must always be placed after 咁 (gam3).

2. Benchmarking
When you use this pattern, the object (the person or thing after 冇 (mou5)) is treated as the 'standard' or benchmark. For example, in 'A 冇 B 咁高', B is the standard of height that A fails to reach.

3. Negating a 過 (gwo3) Comparison
This pattern (along with 唔夠) is the standard way to negate a 過 (gwo3) comparison. For example, the negative of 'A 高過 B' (A is taller than B) is 'A 冇 B 咁高' (A is not as tall as B).

4. Omitting the Object
If the context is already clear, you can omit the object of comparison entirely. In this case, the pattern means 'not that' or 'not so'. For example: 呢件衫冇咁貴 (nei1 gin6 saam1 mou5 gam3 gwai3) — 'This shirt isn't that expensive'.

5. Usage with Verbs
While most commonly used with adjectives (stative verbs), it can also be used with verbs of feeling or mental states, such as 想 (soeng2, to want). For action verbs, you typically need to use the particle 得 (dak1) after the verb before applying this pattern. For example: 我食得冇佢咁多 (ngo5 sik6 dak1 mou5 keoi5 gam3 do1) — 'I don't eat as much as him'. Alternatively, the benchmark noun can be placed before the verb: 我冇佢食得咁多 (ngo5 mou5 keoi5 sik6 dak1 gam3 do1).

6. Comparing Nouns
When comparing quantities of nouns (e.g., 'I don't have as much money as him'), learners often mistakenly put the noun directly after 咁. You must explicitly use the adjectives 多 (do1, much/many) or 少 (siu2, few/little) before the noun. For example: 我冇佢咁多錢 (ngo5 mou5 keoi5 gam3 do1 cin2). You can also describe a specific noun using the structure 咁 + Adjective + Classifier + Noun. For example: 我冇佢咁大個肚腩 (ngo5 mou5 keoi5 gam3 daai6 go3 tou5 naam5) — 'I don't have as big a belly as him'.

7. Question Form
To ask a question using this pattern, use the A-not-A form 有冇 (jau5 mou5) instead of 冇. For example: 你有冇佢咁高？ (nei5 jau5 mou5 keoi5 gam3 gou1?) — 'Are you as tall as him?'.

8. No Degree Modifiers After 咁
Because 咁 (gam3) already functions as a degree marker ('so' or 'that much'), you cannot add other degree modifiers like 好 (hou2, very), 非常 (fei1 soeng4, extremely), or 最 (zeoi3, most) after it. For example, learners must be explicitly told that *我冇佢咁好高 (ngo5 mou5 keoi5 gam3 hou2 gou1) is incorrect. It must simply be 我冇佢咁高 (ngo5 mou5 keoi5 gam3 gou1).

9. Related Patterns
The positive counterpart to this pattern is 有...咁 (jau5... gam3), meaning 'as... as'. It is used to make positive comparisons of equality, often emphasizing that a high benchmark has been reached. For example: 我有佢咁高 (ngo5 jau5 keoi5 gam3 gou1) — 'I am as tall as him'. For neutral equal comparisons, 同...一樣 (tung4... jat1 joeng6) or 同...一樣咁 (tung4... jat1 joeng6 gam3) is also very common.

10. Register
This is a highly colloquial and frequent pattern. In formal written contexts, you might see different structures used instead, but in daily speech, 冇...咁 is the undisputed choice for becoming confident with comparisons.