This paper presents a semantic explanation for the acceptability-unacceptability contrast between complex noun phrases(NPs) with apparently similar syntax. It also tries to present a corresponding semantic explanation for the acceptability-unacceptability contrast between corresponding topical structures with apparently similar syntax. After showing that the complex NPs must be licensed by the characterization condition and the topical structures must be licensed by the aboutness condition, the paper analyzes the semantic identification of restrictives from nonrestrictives. This is closely related to the(dis)satisfaction of the characterization condition and therefore the(un)acceptability of(apparent) recursive complex NPs, as well as the(dis)satisfaction of the aboutness condition and therefore the(un)acceptability of corresponding topical structures in both English and Chinese.