Transitive verbs are not allowed as V2. This is because a transitive verb, which describes an independent event, has its own subject (Agent) and object (Patient). As such, it cannot act as a resultative complement expressing a change of state. When they do occur in a RVC as V2, for example in ‘tīngdǒng’ (listen understand = understand as a result of listening) and ‘xuéhuì’ (learn-can = learn), however, they are in fact accommodated under the notion of ‘change of state’. Thus the verbs ‘dǒng’ (understand, know) and ‘huì’ (be able to), when acting as V2 in a RVC, indicate a change of mental state from the previous state of being ignorant to the subsequent state of being knowledgeable, in this sense of transformation, they have become Achievements. This is confirmed by the fact that they can occur with the inchoative aspect particle ‘le’.
Zhāng Sān yǐqián bù dǒng Yīngwén, xiànzài dǒng le.
(Before Lisi didn’t know French, but now he knows.)
1a’ * 张三以前不懂英文，现在懂。
* Zhāng Sān yǐqián bù dǒng Yīngwén, xiànzài dǒng.
1b. A: 弟弟会游泳了吗?
Dìdi huì yóuyǒng le ma ?
(Can the younger brother swim now?)
(He can now.)
(1a’) and (1b B’) are unacceptable, because the verb ‘dǒng’ (understand) and ‘huì’ (be able to) in the contexts both signal a change of state, rather than a state, hence they must be combined with the inchoative aspect particle ‘le’.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.