In the logics of belief, the possible worlds semantic (Kripke 59) is attractive, for its formal elegance and for the intuitive notion of making a discourse, not only of the present world but for any possible world. The fundamental limitations are the logical omniscience and the ideal reasoning. We consider that there is confusion in speaking about them. In this paper we analyze and propose a general characterization of them. We propose a constructive definition of relation of possibility between worlds, such that the possible worlds are a result of a process. The knowledge and belief in a world w, depends of the worlds generated --during the process-- from w. Then they are essentially different: they are more realistic than those defined in the logics of belief with possible worlds semantic.