The main problem encountered when starting verification of goals for some formal system, is the ambiguity of those goals when they are specified in natural language. To verify goals given in natural language, a translation of those goals to the formalism of the verification tool is required. The main concern is to assure equivalence of the final translation and the original. A structured method is required to assure equivalence in every case. This article proposes a goal formalisation method in five steps, in which the domain expert is involved in such a way that the correctness of the result can be assured. The contribution of this article is a conceptual goal model, a formal expression language for this model, and a structured method which transforms any input goal to a fully formalised goal in the required target formalism. The proposed formalisation method guarantees essential properties like correctness, traceability, reduced variability and reusability.