を + する: what are the rules?
I thought that を was pretty much optional in combination with する - so for example you can either say しごと します or しごとを します.
Yet Duolingo demands the を in certain instances. In Dates 2, there is the sentence
す来年、何をしますか。(What will you do the year after next?)
and if you leave out the を it is marked wrong, even though in other sentences Duolingo doesn't seem to care.
Question: is the combination 何を a special case, maybe?
Hi! You can add ～する to the end of certain foreign loanwords and compound nouns of Chinese origin. For example,勉強(study) becomes 勉強する(to study). These are called nominal verbs. This does not work for every foreign load word and compound nouns of Chinese origin. For example, you cannot add する to 会議(meeting). You have to do 会議をする(to hold a meeting). So, most nouns that can be turned into nominal verbs can also be used as a direct object of する.
So for you original question, 何を is not a special case. You cannot say 何します(to do what) because that makes no sense. You have to say 何をします because 何 is the direct object of する. Hope this helps!
Because 何 is indefinite and not connected to any action. しごとする is basically an action as a whole. It means "work," but literally means "do work/job." The する sorta loses its meaning as "do" and blends into しごと. しごと kinda becomes part of the verb itself. With 何をする, you want to keep する's meaning as "do," so you can ask "what do/will you do?" so you keep them seperate with particles (the direct object particle in this case, since you're asking for the thing being done). Also, if you try to turn "what" into a verb, that just makes no sense. "What" isn't a word you can just turn into a verb.
I guess that means that しごとをする carries a nuance more akin to "do work" and しごとする is more akin to just "work," but it's essentially the same thing.
I hope that this makes sense. Good luck!
But what about all the activities that get by without を? You can't just "tennis"! So that muddles things up for me. I think for now I'll just try and remember that 何 needs an を (and かいぎ does too? How is that different from tennis? Aaargh!) At any rate, thank you for all your explanations!
Because "tennis," the game, is linked to a clear verb, "playing tennis." You are "doing tennis," or since it kinda blends into the verb, "tennis-ing." Sure that sounds weird in English, but you can kinda see what it means. You can't do that with "what." "Doing what" (seen as an action as a whole and not as an inquiry) and "what-ing" just make no sense, you can't sorta infer a meaning.
I wouldn't quite say that they're their own verbs or even compound words. "Words" in the western language sense doesn't exactly move over to a language like Japanese. They are simply nouns that can be done (or turned into verbs) by adding する.
As far as your question is concerned: 何する doesn't make any sense, but is made up of two "words": 何 (what) and する (do). It would be almost literally like saying "Do what." (not a question, just a statement). Even adding in を wouldn't work.
To say "to do/doing something" you have to say 何か（を）する. 何か (something) + を (direct object indicator, sometimes dropped) + する (do). If you want to know what someone is doing you could use "何をしますか" which literally means "What (are you) doing?"
This is in reply to the question in
Although there is a theory that nouns implying an action can follow the N +する pattern to become a verb, I am not really convinced. We say 食事する(しょくじ)、料理する(りょうり) but it is weird to say ご飯する(はん). Personally I do not see a clear deferentiation in their noun roots. Probably there was such rule in the past, but Japanese language is changing rapidly, that rule, if it existed, does not really hold anymore nowadays. New verbs are being formed in various unprecedented ways, even only る rather than する is added. So we have OLする、デニる、etc. Thus there is really no need to stick firmly to a rule or to feel uneasy about it.
Not all Japanese would actually feel a difference between N をする and Nする。So when you are sure, say Nする; when you are not, always go with the を. You won't get any problem. If you want to learn, get a good dictionary. When you look up a noun, it is indicated if する can be added to form a verb. The mark may be サ変(へん)、スル、etc. depending on the publisher.
Noun + します actually should not be understood as an option of doing without the を particle. It is rather a form to turn a noun into a verb. In this way it should be easy to understand why 何します is not acceptable as 何 is not a noun. It will also help you further to understand why some other similar phrases are not acceptable, simply because those nouns are not usually turned into verb form.