The article presents some problems of the notion of mathematical demonstration in the second Wittgenstein's Philosophy. The start point is the refuse to the distinction between possibility and actuality in the normative context. It argues that the reason for this refuse indicates some tracks for a dissolutive approach for the presented problems. The steps of a proof in mathematics cannot be understood as a justification for any independent additional determination. The reason for this is the necessity involved in the proof. Then, this impossibility cannot mean the rejection of the necessity in question. In spite of this and additionally, the work emphasizes that, if the problems left without solution for the Wittgenstein's approaches make room for the attribution of an apparently unreasonable position to the author, this does not cancel the arguments developed by him against the opposed positions. Thus, we have two problems, since we cannot refute Wittgenstein by the force of the unreasonability attributed him and we cannot too cancel such unreasonability for the force of his arguments itself.
