What “shall,” “should,” “may” and “can” mean in a standard: “The record shall be retained” and “the record should be retained” seem very similar, but do not mean the same thing. It is these words that tell us if a statement is a requirement, a recommendation, permission, or possibility. It is easy to miss them and read right past them, turning an optional statement into a required action, or vice versa.
Here is an example. Look at the following four sentences. Highlight only the key verb: “The process owner shall approve the procedure,” “The checklist should include a review date,” “The reviewer may request additional evidence,” and “The system can generate a revision log.” Describe the action that is being allowed or required by each sentence. This type of exercise will train you to categorize the statement before you even think about the implementation.
Shall is generally used for a requirement. When we say that an organization shall take some action, then the organization should take that action in order to be conformant. A good interpretation would identify the actor, the action that must be taken, and possible evidence. For example, if we have a statement that a procedure shall be approved prior to use, the evidence could be an approval signature, or the document being controlled.
Should is generally used to express a recommendation. However, a recommendation may still be helpful, but should not automatically be inserted into a checklist as a pass or fail item. May is generally used for permission; that a person or organization is permitted to take an action. Can is generally used for possibility; what a system, process, or method is capable of doing. Neither will create an obligation.
When a sentence is long and complicated, these statements become more difficult. Sometimes a sentence will contain many actions, examples, and explanations, and only a portion of the statement is controlled by shall. Reword the sentence into simpler terms. Keep the required action separate from the supportive text. Do not replace shall with words like “could” or “is encouraged to.” On the flip side, don’t change should to must just because the recommendation seems reasonable.
Lastly, before adding a statement to your procedure or requirements checklist, take a moment to identify the controlling verb and define its purpose. Is it a requirement, recommendation, permission, or possibility? If you cannot answer this question, go back to your source material and re-read the definition, context, and related clauses before you assign responsibility or look for evidence.