[Context and motivation] To formulate a formal require- ment in a natural language with a restricted English Grammar, such as the pattern language of Konrad and Cheng, give us the possibility to combine human intuition and the rigour of a machine. [Question / problem] The question arises to what extent the intuitive understanding of such a requirement is correct. [Principal ideas / results] We present an empirical study to address this question. The existence of a formal semantics allows us to use the machine as an objective judge to decide when the intuitive understanding is correct. Both, the requirement and the behaviour have a machine representation, and an algorithm exists to decide whether the behaviour satisfies the requirement. Thus, we only have to compare the decision of each participant in the study with the algorithmic decision. The study confirms empirically the practical usefulness of formal pattern languages in that the intuitive understanding matches the formal semantics in the general cases. The study reveals that a number of phrases of interest represent critical border cases where even a prior exposure to formal logics is not a guarantee for the correct intuitive understanding. [Contribution] We start what we hope will be a longer series of investigations of the match between intuitive understanding and formal semantics for classes of requirements that have both.