In the sentence “他喝了一口水” (t¯a h¯e -le y`ı-k˘ou shu/ He took a sip of water.), -le is viewed as a inflectionally bound morpheme affixed to the verbal stem he(喝). It is a perfective marker indicating the realization of the event “taking a sip of water.”
On the other hand, in the phrase “草草了事”(c˘ao -c˘ao li˘ao shì/ To finish a task hastily), -le is a free verb meaning “to finish.”
(According to Chaofen Sun, the inflectional aspect marker -le is a phonologically reduced form that has been grammatically changed over time from a Middle Chinese morphologically free verb “to finish.” Nevertheless, this kind of phonological and morphological change is not reflected in Chinese writing.)
Reference: Chinese: a linguistic introduction by Chao Fen Sun
