It’s surprising that people routinely get things wrong here.
If there are two subjects to your sentence, separated by or, the verb should take the number of the subject that is closest to it: Mother or children are to die BUT Is the mother or the children to die? You could also rewrite the sentences to avoid the issue: Mother or children must die, Must mother or children die?
Is it The committee is or The committee are? There are two schools of thought.
In the US, words like committee, firm and board are invariably treated as singular: the entity not its constituent parts.
There is a good case to be made, however, that these words can take a plural verb when you want to emphasise the members of the group over the totality: The [individual members of the] jury are casting votes BUT The jury [the body] reached its verdict; The board has agreed on most issues BUT The board are unable to reach consensus on the thorniest question.
Fowler’s Modern English Usage supports this view, with these examples: The Cabinet is divided (on the grounds that the whole logically precedes division) but The Cabinet are agreed (because it takes two or more individuals to agree). Fowler notes that the distinction can be ‘delicate’, and is one that few will bother to make; ‘any attempt to elaborate rules would be waste labour.’
Current practice in the UK probably goes further than what Fowler had in mind, with results that have some logic but which look outlandish to North Americans. Recent examples from the British press: The digital music giant [Apple Inc.] are unlikely to be impressed by the demand [from Adele to have hard copies of her new album available in Apple stores); Australia [the Australian rugby team] deserve to win the final.
Whichever way you go, make sure you are internally consistent: don’t say During their time in office, the Government has …
This is singular or plural, depending on the context. I looked for books on this subject in the library, but there were none BUT I asked for a volunteer, but none was forthcoming. I would say None of the partners is attending, on the assumption that none is a proxy for not one.
Don’t let extra words throw your sense of number off.
This sort of thing is wrong (but very common): One in five kids who grew up with the internet believe all of it is true (from Quartz). So is this (from the Globe & Mail): Wave of refugees show Europe’s disarray in tackling the crisis… (the verb must be shows, unless you’re taking the position that wave is a plural collective).
There is, there are
There may seem like a singular subject in constructions like There is no excuse for getting this wrong, but it’s not the subject of the sentence (excuse is, actually). There is, in grammatical terms, an expletive (but not the NSFW kind).
As a result, whether it’s there is or there are depends on what follows. So, There is no excuse but There are many things to consider.
Things that aren’t singular
Criteria: We get this from Greek. Singular criterion, plural criteria. Associates are evaluated according to these criteria …
Data: Latin. Singular datum, plural data. The economic data indicate …, as the Financial Times would correctly say. (And it’s best pronounced DAY-ta not DAH-ta.)
Media: More Latin; plural of medium. The medium is the message, and social media are proving that point.
Phenomena: Greek again. This is plural; the singular is phenomenon.
Things that aren’t plural
Biceps: Latin again. Routinely treated as a plural, but it’s not. The correct plural is bicipites, but your trainer is unlikely to understand that; bicepses is better (although it may still attract funny looks).
Kudos: Those pesky Greeks. It means ‘praise’ (singular), so it’s incorrect to say kudos go to so-and-so; and the second syllable rhymes with ‘loss’ not ‘rose’.
Quadriceps: See biceps.
Shambles: Something is a shambles or in a shambles not in shambles (shambles is singular; it means slaughter-house; figuratively, a scene of disorder or devastation).
Triceps: See biceps.
Things that could be either
Forceps: Both singular and plural.
Innings: Both singular and plural. The US singular form inning is a semi-barbarous back-formation.
Lots: There is lots to do in New York BUT There are lots of things to see there.
Things that don’t have a singular form without –s (or don’t usually)
Amends, cahoots, clothes, glasses (in the sense of spectacles), loggerheads, pants, scissors, shenanigans, shorts, smithereens, spectacles (in the sense of glasses).
Trousers is not generally seen without a final S, but one does say trouser-leg, trouser-pocket and trouser-press; and thank-offering is a survival of the obsolete singular thank (a grateful or kindly thought).
Next: e-mail pointers for the millennial generation (and others).