Expressing Obligations and Prohibitions


Provisions creating obligations in new legislative texts are ordinarily to be drafted using “must”.

Provisions creating prohibitions in new legislative texts are to be drafted using “must not” or the verb “prohibited”.  (Prohibitions are a kind of obligation, an obligation to not do something, but as drafting considerations for prohibitions are different from those for positive obligations, they are treated separately in this note.)  “May not” and “no person may” are not to be used to create prohibitions.

The auxiliary “shall” is not to be used, because of its legalistic tone, its rarity in Canadian English outside legal documents and the multiple meanings that have been ascribed to it in legislative texts.[1] However, when an existing text that contains “shall” is being amended, “shall” may be used in the amending text to preserve consistency, if there is no opportunity to remove “shall” generally from the existing text.

“Must” can sometimes be linguistically inappropriate as a replacement for “shall”.  For instance, a provision such as “There shall be a corporation to be known as XYZ” yields something that sounds wrong if “must” is substituted for “shall”: “There must be a corporation to be known as XYZ”.  If “must” appears to be the wrong word, “is to” can often be used instead: “There is to be a corporation to be known as XYZ”.  Alternatively, some other redraft might be possible: “The XYZ corporation is established”.

It is appropriate to use “must” to impose an obligation on a Minister or the Governor in Council (if, as a matter of policy, that is what is to be done).



“Must” is widely used to express obligation and has long been recognized as being capable of creating legislative requirements.  However, this usage in federal legislation was at one time restricted to non-penal provisions and to sentences in which the subject was not a person. 

“Must” is extensively used in the legislation of other jurisdictions, notably Australia and at least three Canadian provinces (British Columbia, Alberta and Manitoba) that have amended their Interpretation Acts to state that “must” is to be interpreted as imperative.  The UK Office of Parliamentary Counsel has also recognized its use.  There is no case law casting doubt on the effectiveness of “must” to create obligations and prohibitions. The Australian Plain English Manual contains apt words with regard to imposing obligations on Ministers or the Governor in Council: “We shouldn’t feel any compunction in using ‘must’ and ‘must not’ when imposing obligations on the Governor-General or Ministers, because ‘shall’ and ‘shall not’ were acceptable in the past.”[2]  Indeed, in Canadian federal legislative texts, the words “the Minister shall” are currently used in over 300 statutes and in over 200 regulations, and “the Governor in Council shall” in over 100 statutes and in seven regulations.  For that matter, the words “the Minister must” are currently found in over 40 statutes and in over 30 regulations, and the words “the Governor in Council must” in four statutes (but not in any regulations).[3]


There are several ways to draft prohibitions:

Prohibitions must not be drafted as

Not only is “No person must” rare in common usage, but it is ambiguous about whether it means that the thing is prohibited or is merely not obligatory.

“May not” and “no person may” must not be used to create prohibitions.  “May” in the positive has quite a different meaning from “shall” or “must”; however, the meaning of these words in common usage is more or less the same when they are made negative: that something is forbidden.