Most current aspect composition mechanisms rely on syntactic references to the base modules or wildcard mechanisms quantifying over such syntactic references in pointcut expressions. This leads to the well-known problem of pointcut fragility. Semantics-based composition mechanisms aim to alleviate such fragility by focusing on the meaning and intention of the composition hence avoiding strong syntactic dependencies on the base modules. However, to date, there are no empirical studies validating whether semanticsbased composition mechanisms are indeed more expressive and less fragile compared to their syntax-based counterparts. In this paper we present a first study comparing semantics- and syntax-based composition mechanisms in aspect-oriented requirements engineering. In our empirical study the semantics-based compositions examined were found to be indeed more expressive and less fragile. The semantics-based compositions in the study also required one to reason about composition inte...