Insert '得' (can) or '不' (cannot) between a verb and its result/direction complement to express possibility: 看得懂 (can understand), 看不懂 (can't understand).
'了' read as 'liǎo' acts as a potential complement showing whether an action can happen: 去不了 (can't go), 走不了路 (can't walk), 耽误不了 (can't delay).
The affirmative–negative question formed by pairing the positive and negative forms: 去得了去不了？ (Can you go or not?), 回得来回不来？ (Can you get back in time or not?).
A rhetorical question that stresses a negative: 这么早，怎么起得来呢？ (So early — how could anyone get up? = definitely can't).
An adverb expressing a guess with a worried, hesitant or polite tone: 他恐怕去不了 (I'm afraid he can't go).
A spoken filler used when the speaker suddenly remembers something else or wants to change the subject.
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