"Two birds are flying in the sky."
Not in this case. そらをとぶ is a fixed expression meaning 'to fly the sky' or simply 'to fly'.
In English this direct translation might not sound natural. We, however, have the expressions 'sail the sea', 'swim the channel', 'fly the friendly skies', etc. While we can also say 'swim in the channel' and 'fly high in the sky' the intention of the phrase is different.
It might be better to imagine this as 'fly across the sky' instead. On the other hand, attaching a defined counterpart word in English is not necessarily the best way to learn Japanese.
There's no rule that fixed expressions must remain unbroken. A word or clause can be inserted without affecting the meaning of that expression. As を works to link the preceding noun to the following verb there is no problem with comprehension.「空を長時間飛ぶ」「空を鳥が飛ぶ」are but a couple examples that exist in reference materials.
I found an explication in "A Semiotactic Approach to Modern Japanese, page 70 , thesis" saying that this translation should be wrong. In short, they explained that "空を飛ぶ" (そらをとぶ=sora (w)o tobu) means "to fly through the sky" and that "to fly in the sky" has to be translated by "空で飛ぶ" (そらでとぶ=sora de tobu) which is not accepted by the site. "空に飛ぶ" is also a possible form but not for this case because it means "to fly to the sky" and thus not being in the sky. This is also taken from a book from "Kumo, Susumu" written in 1973 "The structure of the Japanese language. Cambridge, Mass, ... The MIT Press, pages 96-102" as said in the thesis. But i do not have this book and i cannot verify.
Yes, you are right, his name is Kuno, sorry for the typo... But "aren't likely" does not mean that it is wrong and instead of refusing it, it could be better to accept and explain what you said about japanese usage because it is grammaticaly correct and means the same. On the opposite way (tranlating japanese to english), as the aim of this test is to learn japanese and not english, i thing that (all, as much as possible) gramatically correct english sentence that have the same meaning whithout considering if english speakers are or not likely to use it should be accepted, because here what seems essential is to verify if you understand japanese and not if you are using the sentence commonly used in UK/US or not. In the "learning english" test it may be different, but not in the "learning japanese" test. But I understand that it cannot be exhaustive.
Japanese often uses 'counters' to indicate the number of something. Flat objects use まい, long and thing objects use 本, and in this case birds (along with rabbits) use わ.
1 bird 一羽（いちわ）のとり
2 birds 二羽（にわ）のとり
There are many counters and resources can be found to memorize them. Suggest you start here for some background.
It is necessary. In particular, countable nouns are normally separated from other nouns by the particle の when the counter precedes what is being counted. You can think of it as similar to the function of 'of' in English.
When the counter follows what is being counted, the の can often be dropped. 二羽の鳥 = 鳥二羽. That being said, 鳥の二羽 would also be fine grammatically, but as there is little possibility for confusion, the の would normally be dropped.
Finally, にわとり (鶏) means chicken. 二羽鳥 would seem to read as 'two-feathered/two-winged bird'. The separation created by の helps to clarify the fact that these two nouns are separate.
空を飛ぶ is a set expression, meaning to fly (the sky).
を normally occurs directly before the verb, to mark the direct object (Throw→the ball / Fly→the sky). If there is another word between を and the verb, it would usually be marked with another particle, such as で to mark the words function (Throw→the ball→with one's right hand / Fly→the sky→on two wings).
二羽 can mean either two (birds, rabbits, etc.) or it can mean 'two wings', depending on context and grammar. Your 二羽 combines with the verb 飛ぶ to make the composite noun-phrase 'two-wing flying' (二羽飛び）. As it is now a noun-phrase, the conjugated form would incorporated into a sentence as 二羽飛びをする, where (again) を marks the object (To do two-winged flying). On the other hand, you could insert で, and have 二羽で空を飛ぶ or 空を二羽で飛ぶ, which would mean 'fly the sky on two wings' , which would not be the correct translation.
To use a similar structure:
①二人の男が/ボールを/投げます。Two males / throw / a ball.
②男は/ボールを/二人で/投げます。The male(s) / throw / a ball / as two (together)
③男は/二人で/ボールを/なげます。The male(s) / as two (together) / throw / a ball.
④男は/ボールを/二人投げ/します。The male(s) / a ball / together-throw / do.
As you can see in sentence ④, the action has been changed from 'throwing a ball' to 'playing catch', where 'playing catch' is considered a noun-phrase. In this example the distinction is subtle, but the meaning is different and is more noticeable when discussing flying birds. Simply by adding a particle (compare sentence ④ to sentence ②) and of course correcting the conjugation, the meaning can change quite a bit.
*I don't know whether this is more helpful or confusing. Hopefully the former:)
I know this answer is rather old, but I had to respond because I'm pretty sure this is really wrong in several ways.
First, 空を飛ぶ is not particularly a fixed expression, any more than many other constructs with motion verbs which take direct objects (which most can), and there's no requirement that it needs to be kept together in the sentence. It is, perhaps, a bit more commonly said that way, but that's it.
More importantly, however,「二羽」(にわ) does not mean "two wings" (at least not in Japanese). That would need to be「二つの羽」(ふたつのはね). Even if it did somehow mean that,「二羽飛び」would still not mean "two wing flying", because for that you would need a particle (で), which is not present. (And actually,「二羽飛びをする」is even more grammatically wrong in yet different ways (as is「投げします」, for that matter), but I won't even try to get into all of that right now..)
"Birds are flying with two wings"
"Two birds are flying"
Putting 二羽 in front of the verb like this is perfectly fine, and this sort of thing is done all the time, for example:
鳥があそこに二羽います -- "There are two birds over there"
This is because 二羽 is a counter expression, and counter expressions can function either as の-adjectives or as adverbs, so you can either attach them to another noun using の, such as「二羽の鳥」("two birds"), or you can use them as an adverb modifying the verb, as in「二羽飛び」("two (of the birds) fly"). When used as an adverb, they can technically go almost anywhere in the sentence (but right before the verb is the most common place to put them).
So there is actually nothing wrong with「鳥は空を二羽飛んでいます」, and as far as I know no reason why this shouldn't be accepted as well.
(The one nitpick I might make here is the use of は basically makes it seem to say "As for birds, two of them are flying in the sky" (or possibly "Two of the birds are flying in the sky"), suggesting that you were previously talking about birds, or something. It would probably be slightly more natural here to use が in most situations, if you were just bringing up birds for the first time (「鳥が空を二羽飛んでいます」-- "There are two birds flying in the sky").)
Or to put it another way, as it stands the unstated topic of the of the sentence is something like what's going on in the world around me. There's a couple birds flying overhead. With your は the topic becomes two birds, and the sentence tells about the two birds. "As for the two birds, they are flying through the sky."
One important thing to understand about は vs が is that (pretty much the same as saying "as for" in English), the topic (は) can only be used for things which are already in the "realm of discourse". That is, for things which have already been previously mentioned or which people would logically expect to be something to be talking about in this case. So if you use は here, it basically means "As for birds (in general, which we were previously discussing)", or "Regarding the birds (which had previously been mentioned)", or possibly "As for birds (in contrast to something else we had been discussing, like, say, dogs)"
But if you hadn't previously been discussing birds, and there's no obvious reason to be talking about them based on previous context, then は doesn't really work.. it's like just saying "As for the birds, ..." out of the blue in English. A listener is likely to be thinking "Wait a minute, what birds? Did I miss something somewhere?".
So if you're just bringing up birds for the first time, you need to use が here instead, which basically says "There are two (previously unmentioned) birds flying in the sky".
So I think there are a whole bunch of problems with this sentence, and I'm not sure where exactly to start:
- The use of を with 鳥 says that something is being done to the birds (by someone else), not that the birds are doing something (that should use が (or possibly は)).
- The には particle (which is a form of the topic particle は) cannot be placed after を. I'm wondering if this was actually supposed to be 二羽 (にわ) instead? (には and 二羽 are pronounced the same, but mean completely different things)
- I have no idea what 習 even is. From what I can tell, that (by itself) is not even actually a Japanese word.
- There is nothing in this sentence that has anything to do with flying at all.
So this sentence, as best I can piece together, says something akin to "In the sky, as for at/by (something being done to) birds, 習 exists."
How would you read it, and what would it mean? Especially what is 習がいます and how would you do it to a bird? foogod points out that 二羽 would be にわ in kana nowadays. I automatically took には to be "two birds," partly because that is how it was written in kana in my early days with Japanese, partly because it couldn't be particles after を, where も is the only particle that commonly occurs there. A few others, such as だに and さえ(さへ to my old eyes), might be found there occasionally, and ば used to be common, but that was before even my time.
Even if you did, it still wouldn't really say quite the same thing. It really says more "(I) am letting loose two birds to fly in the sky", I think.. (or possibly, "(I) am hurling two birds into the sky"(!) )
Anyway, yeah, it needs to use が to say that the birds (subject) are the ones doing the action (flying in the sky). However, you can actually also say:
(personally, this feels to me a bit more like saying "There are two birds which are flying in the sky", instead of just "Two birds are flying in the sky", but it's only a subtle difference, and I'm also not a native speaker so I may be wrong on that point anyway)
I tend to agree but would drop the "which are." "There are two birds flying in the sky." I might also add a は after 空で. But Duo's version seems more natural.
Belatedly it occurs to me that your first paragraph might be directed at my comment. If so, I strongly disagree with that part.
It also occurs to me that if one were to use「飛ばす」then it should also be using「空に」instead of「空で」. 「空で」would imply that you are located in the sky while you are letting/making the birds fly (I suppose this could work if you were somehow riding on the birds and piloting them, but that's the only case I could see where it would make sense to say that).
Well, really "There are two birds flying in the sky" could be a translation for either form, depending on the context.. (but then "There are two birds which are flying in the sky" could be translated a couple of different ways in Japanese too).. it's a little tricky to explain these sorts of nuances with sentences out of context..
But my point was really that I think that using 二羽 as an adverb in front of the verb puts a bit more emphasis on the "there are two of them" (not one, not three, etc) part of things (but it's not a really huge difference, just a slight difference in feel).
My first paragraph actually was directed at your comment, yes. 「飛ばす」does not really mean "to fly". It means "to make fly" or "to let fly". Therefore I think if you were to use that verb, in this case it would probably be interpreted as meaning releasing birds (so that they could fly in the sky), or possibly somehow "piloting" birds in some way (but you would probably need some context to explain how that would work). However, it is also used to mean "to throw/hurl/launch/etc" something, so it could also potentially be interpreted as propelling birds bodily into the sky in some way, etc, depending on the context. In any case, it really would not mean the same thing as「飛ぶ」does, and would not be a correct translation of this sentence, IMHO.
You seem to be fluent in English, so it's odd that you don't seem to understand that "flying a bird" like a kite or a plane is not actually something that would actually make sense to do in most situations, so people would not actually say that.
Without context, therefore, that sentence would likely not be interpreted that way. It would more likely be interpreted in the "releasing" sense which is a thing which people sometimes do.
Please read what I wrote. I did actually say that it could imply piloting the birds somehow, but you would need a particular context to make it mean that.