Compulsory (“Required; obligatory; mandatory”), mandatory (“Obligatory; required or commanded by authority”), and obligatory (“Imposing obligation, morally or legally; binding”) have related and similar meanings.
There are many examples where one of those words could be used in place of another, but in some areas, set phrases arise; for example, compulsory education, compulsory service, mandatory minimum sentences, mandatory retirement, obligatory treatment. For further examples, click the book links at ngrams for compulsory,mandatory,obligatory. Also see ELU question Are the words “mandatory,” “obligatory,” and “compulsory” interchangeable? and similar questions at other sites (1, 2, 3, 4, 5). The differencebetween page is quite informative:
Mandatory and Compulsory are two words that are often confused when it comes to their meanings and connotations. Strictly speaking, there is some difference between the two words. The word ‘mandatory’ is generally used in the sense of ‘binding’. On the other hand, the word ‘compulsory’ is generally used in the sense of ‘essential’. This is the main difference between the two words.
It is important to note that anything that is mandatory has the quality of binding the doer to the work. On the other hand, anything that is compulsory has to be essentially done without postponement. The word ‘compulsory’ often refers to things or requirements. On the other hand, the word ‘mandatory’ often refers to conditions. ...
However you look at this question it's not easy to answer
Whereas ignoring it is the easy option
However, neither will keep me awake at night
I'd always use "whereas" as the second part of a comparison. "however" could also be used in this way. Often "however" would have a comma after it when used as the second part of a comparison.
I take "however" as something like "how ever you take the meaning of this" .
OTOH "whereas" is something like "in contrast to the previous opinion"
Best Answer
Note that "What for?" is informal/conversational.
"What Purposeful Reason?"
"What for" denotes a purposeful reason, while "Why?" can be used for causes, reasons, or explanations.
Why? OR What for? (Purpose): "To make money."
Statement 2: "Things fall."
What for (purpose only!): "Who knows? God? Quantum Multiverse? That may not be answerable."
Statement 3: "I exist."
Variations can be created by sentences like "What is $NounPhrase$ for?" For example, if one is in a new car with a salesman, one can ask "What is that button for?" In this case, the question is asking for the functional purpose of the button. Also, "What is math good for?" is asking for suitability for a purpose.
"What for!?" -- Emphasis / Surprise / Suspicion
"What for" can lend itself to more emotion than a simple "Why", adding surprise, suspicion, or just more emphasis. In this case, "what for" can be asking for an explanation just like "why":
The emotion behind "What for?" can also be suspicion or interrogation. There can be a bit of eye squinting or head tilting:
"Can I ask you your name?"
"Ummm. What for?" (Suspicion)
"For what?" -- Identifying ambiguity.
"What for" can also be used to mean "For what?" in order to identify an ambiguous reference. The emphasis is on replacing the "what" with the named item rather than replacing the "for" with the named reason:
Here's another one:
Both "what for" questions could be asking for purposeful reason. For example, in the 2nd case, the reason could have been to clean the shelf. But the answer given in the 2nd case was an identification of the object desired.
Also, "What am I responsible for?" is asking for identification of responsibilities. It is like "For what am I responsible?", but the fronted what sounds more natural.