The purpose of this paper is to observe the properties of undetached relative clauses qualifying nouns determined with the indefinite article A in the framework of the theory of enunciative operations. In this framework, determination is seen as a process through which indeterminacy is eliminated and occurrences are stabilised. We have observed the interaction of indefinite determination with the qualification expressed in the relative clause to sort out when the relative clause gives the conditions for determination in A and when its role is to qualify an occurrence whose conditions of existence are to be found elsewhere in the utterance. This contributes to explaining why undetached relative clauses with an indefinite antecedent are problematic vis-à-vis the classical distinction between determinative and appositive relative clauses.