SHALL
When used as an auxiliary verb, shall, according to Webster's Online Dictionary, “denotes a requirement that is mandatory whenever the criterion for conformance with the specification requires that there be no deviation” (2). This word implies obligation and is traditionally used by laws and regulations. For example, Chapter V of the Federal Food, Drug, and Cosmetic Act (FD&C Act), “Drugs and Devices,” begins with the following:
“A drug or device shall be deemed to be adulterated –” (3).
Similarly, the FDA’s regulations frequently use shall to indicate mandatory requirements. In CFR - Code of Federal Regulations Title 21, Part 803, the regulation for medical device reporting, the English reporting requirement states:
“All reports required in this part which are submitted in writing or electronic equivalent shall be submitted to FDA in English” (4).
SHOULD
On the other hand, should “denotes a guideline or recommendation whenever noncompliance with the specification is permissible.” When used as an auxiliary verb, it expresses “a conditional or contingent act or state … or moral obligation” (5).
The statement “Incoming materials shall be inspected before they are accepted in warehouse” is mandatory. All incoming materials must be inspected before they are accepted in warehouse. A deviation causes a noncompliance with the document.
In contrast, “Incoming materials should be inspected before they are accepted in warehouse” is a recommendation by the document writer. It allows the document users to make their own judgment calls.
In reality, the incoming materials will most likely be inspected before they are accepted. However, the document users at any time can make a deviation based on the specific situation, as long as the decision making is reasonable and logical. (Recall also that the word should does imply moral obligation.) Such deviation does not violate the document’s requirement.
Because of the built-in flexibility of the word, if the document writer intends to mandate a requirement, should is not an appropriate choice.
