Perfective aspect particle le 了 (or verb-suffix le 了)

The perfective aspect particle le 了 marks the perfective state of an action. It indicates that the action is completed. The aspect particle le 了 is placed immediately after the verb. It is also called the verb-suffix-le 了 or verb-le 了. By 'perfective state' we mean that “the action as represented by the verb has attained its completion by a certain reference point in time. The Chinese verb-le serves to mark this perfective aspect. It is an aspect marker and not a past tense indicator. The verb-le can appear with a future action, a present action, or a past action, as long as the context calls for its use.” (H. S. Cheung: 1994, p. 207).

1. 
   Wǒ mǎi-le sān běn shū.
   我买了三本书。
   I bought three books.


Note: The aspect particle le 了 after the verb 'mǎi' 买 (to buy) signifies that the action of buying is completed.


2. 
   Míngtiān wǒ chī-le wǎnfàn jiù qù xuéxiào.
   明天我吃了晚饭就去学校。
   Tomorrow I will go to school after I eat dinner.


Note: This sentence is about a sequence of actions that will take place in the future. The aspect particle le 了 here signifies the future perfective aspect of the action chī 吃(to eat). Chī-le wǎnfàn 吃了晚饭 here means 'after eating dinner'. It is the first action in the sequence. It is followed by the second one, qù xuéxiào 去学校, which means 'to go to school'.

However, there are strict restrictions on the use of the perfective aspect particle le 了. First, the verb must be an action verb capable of definite termination. Dispositional verbs may not take a verb-le 了. Second, it is used for bounded events. “An event is viewed in its entirety if it is bounded temporally, spatially, or conceptually.” (Charles N. Li and Sandra A. Thompson: 1981, p. 185). According to Li and Thompson, there are essentially four ways in which an event can be bounded.