In this paper we will try to show that the restrictive clauses limit the scope of their antecedent, but the non-restrictive clauses do not limit the scope of their antecedent. Based on the differences between the restrictive clauses and the non-restrictive ones, we will first propose some fundamental conditions to be restrictive and also to be non-restrictive. And then from the discursive point of view we will try to explain why the restrictive clauses behave differently from non-restrictive ones. It is necessary that this study attempts to deal only with relative subject pronouns, because the choice of the relative clause depends on the discourse element. The focused elements such as quantifiers, undefined, numerals, can be constructed only with restrictive relative, therefore this discursive process allows us to suppose that all the antecedents of the restrictive relative are focused. Unlike the restrictive relative, on the other hand, the non-restrictive clauses have the definite and specific antecedent that plays the role of topic. Finally, from the discursive point of view, we can conclude that the restrictive clauses and the non-restrictive ones depend on the focus and topic discursive category.