The purpose of this work is to study the elements of indefiniteness in Russian complex sentences like Oni brali vsë, čto najdut ‘They took everything they could find’ (lit. ‘…everything they will find’). On the one hand, we are trying to give an accurate idea of the characteristics of the referent which is relativized, and, on the other hand, we are studying the role of the perfective future tense in the expression of indefiniteness. It turns out that the perfective future expresses a special type of iterativity, which we call aleatoric iterativity; the perfective future is only used in distributive situations and is always associated with a variable referent. In addition, this use of the perfective future, like many non-futural uses of this form, bears a modal meaning. The article also defends the hypothesis that the category of indefiniteness is gradual. Formal indicators of the degree of indefiniteness are the correlate to in the main clause and the particle ni before the perfective future-tense verb in the realtive clause.