"Are there two?"
Would there be 'ga' before 'arimasu' if it is a question? Little bit confused ^^;
I believe there is no "ga" seeing as there's no noun. If you were asking about two chairs for example, then you'd have to include the "ga" particle.
I am not sure on how to pronounce "ニつ", would be handy if the application offered to read out the sentence in questions where you provide the Japanese as well.
Before entering the course, (press on the course, but don't start), there is a little lamp. On there, it informs you of what is gonna come up and teaches you a bit how everything works.
This is added recently thanks to the contributors. It is only added for some lessons (at the time of writing) but not all of them. In the past there were no such course notes.
Is there a rule we can use to tell whether 'arimasu' or simply 'imasu' is necessary?
(might be wrong but) arimasu is used when referring to inanimate objects and imasu is used when referring to animate objects
Both are acceptable to use, it would just imply that you were talking about different things. In this specific example, you could use either, since there's no further context.
could you also say "futatsu desu ka?" would that make sense gramatically? just curious
Yes. This is a common practice to omit the verb in conversations if the context is clear.
"Two" is not the subject of the sentence so it cannot be followed by が. "Are there two (of them)?" where "them" is the subject which is omitted.
Given that the Japanese counters change depending on the subject, would it not be imperative to have the subject here? If so, would then が be placed after said counter?
Unlike English, there are absolutely no obligation in Japanese to place a subject or an object in any sentence if the context is clear. Technically only a verb is required, but that can also be omitted in some cases.
- よろしく (only an adverb)
- よい旅（たび）を (only an adverb and an object)
- 気（き）をつけて (an object and a verb in an incomplete clause)
On your point "Japanese counters change depending on the subject," in this sentence 二つ is the invariant form (does not change with the subject). English counters also change with the subject,
- two pieces of cake 二切れ（ふたきれ）のケーキ
- three pairs of glasses 三本（さんぼん）のメガネ
- one teaspoon of sugar 小さじ一杯（こさじいっぱい）の砂糖（さとう）
True, Japanese does like to omit the subject of the sentence. But if you have context, the meaning of a single sentence can change. Simple sentences in the start of learning are all good, but when reviewing it gets a little harder when you know that context is very important. If there is no context it is difficult to accurately translate from language to language. Without it, simple Japanese sentences that only have the verb have little meaning. Assuming the meaning gets us no where as linguists
English does have it's counters, but you can (in some cases) not have the counter as they are implied. Not exactly true with Japanese. As I am currently living here, several of my Japanese friends have corrected me and encouraged me to use the various, if not unending, different counters for the specific objects. So merely stating 二つ when talking about an animal even if it is understood, is strange
Yes, I agree with what you have said - in duolingo it is difficult to imply context, and to avoid generic counters when specific counters are more appropriate.
However, it does not answer the grammatical question "Is it correct to say 二つがありますか ?" - the answer is that it is technically correct, but the meaning is different. I am going into some details.
When a counter acts as a subject (or object), this counter is a specific group where by context it is known to the participants of the conversation. It is very unnatural to use 二つ in this case but I managed to make up one. Please look at the following example:
- ジョンとマリアは私のクラスメイトです。二人があそこにいます。 John and Maria are my classmates. The two are over there.
- A: 部屋に田中さんへのプレゼントが３つあります。そのうち、一つが左の袋にあります。B: では、右の袋にのこりの２つがありますか。 A: There are three presents for Mr Tanaka in the room. Of the three, one is in the left bag. B: Then, in the right bag, are there the remaining two?
When the question says "Are there two?" it implies that the "two" things are unspecified. Otherwise it is better o specify "the two" or "two of them" explicitly to indicate the things are specific and known. When the things are unspecified, the counter cannot act as a noun. It can only act as an adverb, so ２つあります rather than ２つがあります.