The Gary Hinde opinion piece talks to may v shall and such
So I found this on the web --- interesting - (and one would have thought this would have been cleared up 100 years ago)
(note - 46179(f) uses "may" .. no court may ..)
What's the only word that means mandatory?
Here's what law and policy say about "shall, will, may and must."
We call "must" and "must not" words of obligation. "Must" is the only word that imposes a legal obligation on your readers to tell them something is mandatory. Also, "must not" are the only words you can use to say something is prohibited. Who says so and why?
Nearly every jurisdiction has held that the word "shall" is confusing because it can also mean "may, will or must."
Legal reference books like the Federal Rules of Civil Procedure no longer use the word "shall."
Even the Supreme Court ruled that when the word "shall" appears in statutes, it means "may."
Bryan Garner, the legal writing scholar and editor of Black's Law Dictionary wrote that "In most legal instruments, shall violates the presumption of consistency…which is why shall is among the most heavily litigated words in the English language."
Those are some of the reasons why these documents compel us to use the word "must" when we mean "mandatory:"
The Federal Register Document Drafting Handbook (Section 3) states
"Use ‘must’ instead of ‘shall’ to impose a legal obligation on your reader."
The Federal Plain Language Guidelines (page 25) (PDF) referred to in the Federal Plain Writing Act of 2010, compel the FAA and every federal department to "use ‘must,’ not ‘shall’" to indicate requirements.
FAA Plain Language Writing Order 1000.36, (page 4) (PDF) says avoid the word "shall" and use "must" to impose requirements, including contracts.
Until recently, law schools taught attorneys that "shall" means "must."
That's why many attorneys and executives think "shall" means "must." It's not their fault.
The Federal Plain Writing Act and the Federal Plain Language Guidelines only appeared in 2010. And the fact is, even though "must" has come to be the only clear, valid way to express "mandatory," most parts of the Code of Federal Regulations (CFRs) that govern federal departments still use the word "shall" for that purpose.
