 The double aspect doctrine, which applies in the course of a pith and substance analysis, ensures that the policies of the elected legislators of both levels of government are respected.The double aspect doctrine recognizes that both Parliament and the provincial legislatures can adopt valid legislation on a single subject depending on the perspective from which the legislation is considered, that is, depending on the various aspects of the matter in question.In certain circumstances, however, the powers of one level of government must be protected against intrusions, even incidental ones, by the other level.