The States General have an absolute right to information from the government in writing or in person, only constitutionally limited by State interests, such as the national security (Article 68). Doctrine holds that there can also be "natural impediments" justifying that a minister fails in answering questions, such as the circumstance that he simply doesn't know the answer, that he has already answered or that he is about to answer much more completely by issuing a written report on the question. Another doctrinal limitation is the ministerial responsibility: a minister is not obliged to give information about a subject for which not he is responsible but his colleague. Government members have access to the sessions and can freely partake in the discussions (Article 69); they can also be invited to do so by the Houses (Subarticle 2). Such an invitation is in fact an order: government members are not at liberty to refuse. They do however have the right to invite any expert to assist them in the discussions (Subarticle 3). All persons partaking in the deliberations of parliament or in the parliamentary commission meetings have legal immunity regarding any communication they made, either in speech or in writing (Article 71). Otherwise the members have no parliamentary immunity.