In a legal document, “shall” generally means “is required by this rule (i.e., statute, regulation, by-law, etc.) to”. I’ve not seen “should” or “will” used in a legal document, and (unless they were defined within the document) I think they could be confusing: Does “should” mean some ethical requirement that is not legally binding? Is “will” just a prediction about the future?
It’s not really a legal document but rather a guidance document expanding on the requirements of the regulations. I’m trying to get hold of the document itself, I was taking someone’s word that the preamble wasn’t there.
Edit: It’s ok, I’ve found the preamble, “should” means a person is “encouraged” to do something while “must” and “shall” mean they are required to do it.
“Should” should not be anywhere in any type of legal writing – well, perhaps in a memo, sadly it’s probably seen a lot in actual legislation. It should not be in any legal agreement or contract. Should is a conditional phrase (I forgot the technical term for it), which, in of itself, is not necessarily bad drafting. However, it is often used to describe a condition with many other possible outcomes which the document often fails to capture or account for.
I also feel strongly about the unfortunate use of “may” and “will” (more so for the incorrect usage).
I’ll explain more about the document. It’s not a regulation as such. The rules of the air in Australia are set out in a number of regulations. These regulations often have get out clauses such as “unless authorized by the Authority…”. One of the means for the Authority to authorize various things and to expand on the regs is the AIP which is a manual for pilots that provides a mixture of mandatory practices based on the rules, recommended practices, and general information of use to pilots. It is this AIP that has the fuzzy language such as “should”. Although it is tied in to the rules it is probably not the type of legal document you guys are thinking of.
The only legal sense in which I can recall hearing “should” used is as part of the general aspirational guidelines for professional conduct. In Pennsylvania, for instance,
That’s from the preamble of the Rules. You’d never actually be in violation of those guidelines specifically, but of the actual rule that governs whatever conduct you were engaged in (and which would say “shall” or “shall not… unless” or something). This seems roughly analogous to the manual you’re looking at, so it’s possible that they’re using it in the same aspirational sense.
That’s a good point. Generally mandating an action is ok because, as you point out, any rule can be broken for the purposes of avoiding a fiery death, but I think “should” is used when you may use your judgement to do something if, in your opinion, it is just safer.
The example that started this is that the AIP says that aircraft should complete their turn on to final no lower than 500’. Because they use “should” I can come up with several everyday reasons why you might not follow that guideline (not practical given the terrain for one.) If instead they’d used “shall” then the only time you could break the rule would be to avoid turning into a fiery wreck. So if the terrain made it impractical or impossible to complete the turn at or above 500’ you simply wouldn’t be able to operate into the airfield.