In Mandarin Chinese the two lexical items "de" and "bu," when inserted into a verb-verb construction, function as positive and negative potential markers, respectively, Their insertion, however, is not very regular or uniform, because some V-V constructions require their presence, while some others take them optionally, and still others do not occur with them at all. The purpose of this paper is thus twofold: first, to study their distribution, and second, to account for their co-occurrence or nonco-occurrence in the V-V constructions involved. It is claimed here that with the help of the semantic properties of the V-V constructions, we can easily predict where they can be inserted, and where they must be excluded. (Author)