Co-verbs in Mandarin Chinese: Verbs or prepositions?
汉语中的副动词：动词还是介词？
Charles N. Li; Sandra A. Thompson

Abstract 摘要
They are semantically like prepositions, but many of them are homophonous with verbs; because of these two properties, grammarians have not been able to agree on their classification. Since there is an evident similarity of certain co-verbs to verbs being due to the historical evolution of the present-day co-verbs from earlier verbs, the semantic arguments in favor of regarding co-verbs as prepositions are compelling. These arguments include the fact that co-verbs have prepositional meanings, and that sentences containing co-verbs are not two-clause sentences. A comparison with the two-clause ‘serial verb’ constructions in Mandarin makes this clear. The synchronic and diachronic facts regarding Mandarin co-verbs find an exact parallel in the Kwa languages of West Africa.