Interested in Language
Do you come to school by bus or (by) car?
Is 'by' obligatory?
Thanks again, Harry.
No it isn't.
The repetition of by is not required in a list athough you can include it if you want to. Simple lists have an implied header, in this case 'by'. For instance:
"Did you arrive by bus, car, bike, train, plane, or some other method?" is a perfectly acceptable sentence because the list is headed by the word 'by'.
You could say "Did you arrive by bus, or by car, or by bike, or by train, or by plane, or by some other method?" but this has an unnecessary use of words which add nothing to the meaning.
or you could say "Did you arrive by bus, by car, by bike, by train, by plane, or by some other method?"....again unnecessary words, not so many, but still unnecessary.
Lists can take many forms: a common form is to introduce a header, then list the options - that is what the above examples do. Another list form is a key:value list, where although the list has a common theme, each item has a different reason for being in the list and therefore requires a new header for each list item...eg.
This is a list my achievements: sport: I won everthing, drama: ok, english: brilliant.
A list with the same header for each item doesn't need the header repeating.