The Paramountcy Doctrine
The paramountcy doctrine may be stated in this way.  From constitutionally valid power bases  in their own respective catalogues of powers, both Parliament and a provincial legislature  enact valid legislation.  The legislations meet in the sense that they regulate similar activities.  The legislations contradict: in a strong sense the two statutes command a citizen to do inconsistent things and the citizen cannot comply with both statutes.  One statute says “go right”, the other says “go left”, and the citizen cannot go in both directions.  In a weaker version — R. v. Chiasson, (1982), 135 D.L.R. (3D) 499 (N.B.C.A.) affirmed [1984] 1 S.C.R. 266 — the legislations contradict in that the provincial legislation weakens the enforcement or confuses the citizen about the purpose of the federal legislation.  The point, in any event, is that the legislations meet, regulate the same activities, and conflict.  When they do, the federal legislation prevails.