Abstract. A formalization of a logical subset of Goal Structuring Notation (GSN) arguments is presented. The aim is to reveal the conditions which must be true in order to guarantee that an argument thus formalized is internally consistent. These conditions justify a number of systematic questions which must be answered in the affirmative if a standard safety argument based on natural language is to be believed to be free from inconsistencies. The relevance of these findings to the combination of GSN and controlled natural language with first-order logic semantics is discussed.