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.