Double aspect is a legal doctrine in Canadian constitutional law that allows for laws to be created by both provincial and federal governments in relation to the same subject matter. Typically, the federalist system assigns subject matters of legislation to a single head of power. However, certain matters have several dimensions to them such that for one purpose the matter will fall to one head of power, while for another purpose it will fall to the other. For example, highway traffic laws fall into the property and civil rights power of the province but equally can be a criminal offence which is in the criminal law power of the federal government.
The origin of the doctrine comes from the Privy Council decision of Hodge v. The Queen, where it was stated that "subjects which in one aspect and for one purpose fall within s. 92, may in another aspect and for another purpose fall within s. 91".
Matters of double aspect
The Courts have established several matters that are considered "double aspect" and can be legislated by either provincial or federal government. Those matters include:
- Hodge v The Queen (Canada)  UKPC 59,  9 AC 117 (15 December 1883), P.C. (on appeal from Ontario)
- Rio Hotel Ltd. v. New Brunswick (Liquor Licensing Board) 1987 CanLII 72,  2 SCR 59 (29 July 1987)
- R. v. Furtney 1991 SCC 30,  3 SCR 89 (26 September 1991) and Siemens v. Manitoba (Attorney General) 2003 SCC 3,  1 SCR 6 (30 January 2003)
- Attorney General (Ontario) v. Barfried Enterprises 1963 CanLII 15,  SCR 570 (16 December 1963)
- Robinson v. Countrywide Factors Ltd. 1977 CanLII 175,  1 SCR 753 (25 January 1977)
- Papp v. Papp,  1 OR 331
- Multiple Access Ltd. v. McCutcheon 1982 CanLII 1705,  2 SCR 161 (9 August 1982)
- The Attorney General for Ontario v The Attorney General for the Dominion of Canada, and the Distillers and Brewers’ Association of Ontario  UKPC 20,  AC 348 (9 May 1896), P.C. (on appeal from Canada)
- Peter Hogg, Constitutional law of Canada, section 15.5(c)