"I will play with her today."
I think its helpful to use "hang out" instead of "play" here. This sounds really odd in English for adults.
Just learn the structure. You don't need every sentence to have realistic context for every single reader.
"Playing (with someone)" is not the same as "playing something (with someone)". You wouldn't even use あそぶ to translate the latter into Japanese, normally, it'd just be する "do". So those examples aren't really relevant.
Still, while I do think translating あそびます as "play" is a bit awkward in English when talking about adults (who might be e.g. singing karaoke or drinking at a bar), I tend to agree with Frrost that for the purposes of Duolingo it's easier to just accept it... That is, it's up to the maintainers of the Japanese course whether they want to accept things like "hang out" or "enjoy oneself", but I'm fine with them keeping "play" as the preferred translation even if it's kind of translationese. This isn't an English course, after all.
well it also makes you say youre in 4th grade, so its not really that weird
I was imagining something like: speaking of (doing something) with her today, I will play.
Why couldn't this be about kids? Why are you assuming that this is about adults? Am I the only one here who is not an adult?
So why don't they accept "kanojo to issho ni" in this case, but when I take a walk with her, it is wrong to write only "kanojo to"?
"issho ni" means "together with". If they were asking for "I play together with her," you could put "kanojo to issho ni," but since they're only asking for "I play with her," you only put "kanojo to."
Is the は necessary here? I didn't think relative time phrases needed a particle?
は isn't necessary, but it should be there for time and location subjects. The time span of today is the main subject in this case.
You can add a pause after 今日 and it will work fine: "今日、かのじょ と あそびます".
a) That's not what "subject" means in grammar. The subject of this sentence is (the unstated) "I". (This may seem pedantic, but to understand explanations of Japanese grammar it's important to avoid confusion between "subject" and "topic".)
b) As for marking a time or location phrase as a topic with は, that may or may not be appropriate depending on the context. Saying it "should be there" as a general rule is incorrect (though it's true it'll generally work for these contextless examples).
No it isn't but the は kind of adds the meaning of "I will play with her today, but not tomorrow." It makes it sound like you are purposely stating that you will only play with her today.
To anyone who believes 'playing' to be awkward. Go give your inner child a hug and open your mind/heart... next time you 'hit up' your friends, I dare you to ask them if they wanna come over and play or go out and play- WITHOUT any dirty thoughts as thoughts DIRECTLY affect the way our words come out. Try it innocently and I bet they'll laugh and say 'Sure'. Congrats- you'll be bonding even more in no time. Your welcome. ^_^
I was taught that 「かのじょ/かれ」とあそぶ implied a very specific type of "play" and is thus....impolite....
It's Duolingo, don't think about it too much. (It could be taken very inappropriately though, so I don't recommend using this sentence in English or Japanese.)
I'm very confused as for the difference between the "と" and "も" particles. I gather both can construct sets or enumerations, except that "も" can imply the existence of more elements than stated by the speaker. Is that right? Is that the only difference? Why is "も" wrong in this context?