Since Charter, the SCC has determined that any penal law be declared unconstitutional if it is too vague. Challenges can be brought under s. 7. The court will then use s. 1 to determine whether the vagueness is prescribed by law.
R. v. Pharmaceutical Society (Nova Scotia)  2 S.C.R. 606
The twelve accused were charged with conspiracy to prevent competition unduly under s. 45(1)(c) of what is now the Competition Act. Nova Scotia judge quashed the charge on the basis that the word “unduly” made the law too vague. N.S. Appeal Division overturned the ruling.
Is the impugned section of the law void for vagueness?
No. Appeal dismissed.
A law will be found unconstitutionally vague if it so lacks in precision as not to give sufficient guidance for legal debate.
The “doctrine of vagueness” is a principle of fundamental justice (fair notice to citizens, and limitation of law enforcement discretion).
The threshold for finding a law vague is relatively high.
R. v. Heywood  3 S.C.R. 761
The accused was convicted in 1987 of two counts of sexual assault. In ’89, he was charged with vagrancy for being a person convicted of a sexual offence and found “loitering at or near a school ground, playground, public park or bathing area” contrary to s. 179(1)(b) of the Criminal Code.
Is this restriction on liberty in accordance with principles of fundamental justice? Is the impugned section of the law constitutional?
No. Crown’s appeal dismissed.
The law violates the principles of fundamental justice because it applies without prior notice to the accused, to too many places, to too many people, for an indefinite period with no possibility of review. It restricts liberty far more than is necessary to accomplish its goal.
The SCC creates a “doctrine of overbreadth” in this case.
Application to schools and playgrounds is reasonable, but all public parks and bathing areas is overly broad.
This is also an extremely important criterion applying to everything in criminal law.
If prosecution fails to prove guilt beyond reasonable doubt, accused is innocent.
The House of Lords asserted this principle only relatively recently (1935)