G. Verb showing ability or possibility such as néng 能 (able to), huì 会 (know how to), kěyǐ 可以 (may), etc., do not take verb-suffix le 了.

Note: (x) means that -le 了 may not be used there.

  1. Wǒ xiǎo de shíhou huì (x) shuō Yīngwén, kěshì xiànzài dōu yǐjīng wàng le.
    我小的时候会说英文，可是现在都已经忘了。
    When I was young, I could speak English; but I've already forgotten it all now.


  2. Yǐqián zhèi gè dìfang kěyǐ (x) chōu yān, xiànzài bù xíng le.
    以前这个地方可以抽烟，现在不行了。
    Before smoking was allowed here, (but) not any more now.