口 vs. 嘴巴
What is the difference between 口 and 嘴巴?
Why does this sentence 希望我们很快可以再见 use 可以 but not 能? I thought the usage of 可以 is to ask for allowance, while 能 is to show ability? Hopefully, we can (are able to) see each other again soon?
1.) In my experience I use 嘴巴 more often than 口. Although you can find instances of people using 口 in general conversation, I feel like it is more literary, and more often used in Chinese idioms( ie. 口干舌燥，病从口入，等). In many instances 嘴巴 usually seems to refer to the outside of the mouth, the part that you see, while 口 refers to your entire mouth including the inside, although many Chinese don't even recognize this distinction. Many will use the two interchangeably, so needless to say you will be understood regardless of which one you use.
2.) In the second sentence the reason they use 可以 is to say "I hope we CAN meet again" as oppose to "I hope we are able to meet again". Even in English the difference between can and able to is hard to articulate, some may use them interchangeably.
In Chinese it is much the same way, though the impression I get from the sentence above is that using 可以 seems to imply "I hope that, if you are willing, we can meet again". Using 能 seems to imply that "I hope that, if our schedules cooperate, we are able to meet again". 可以 seems to have an element of "choice" to it, while 能 seems to be less about choice and more about physical ability.
口 is just quite a short way to say 嘴巴。 sometimes we prefer to say more than two character to make a word sound clearer. Here are some examples which relate to open or close one's mouth: 開口唱歌／開口大笑：(to open one's mouth and) sing / laugh、 閉口不談：to zip up one's mouth, not to talk about sth、 閉嘴：to shut up one's mouth -[informal]、 and however, while I point to my mouth, I would say 「這是嘴巴」instead of「這是口」
I could not explain it well but I would say if you add 夠 behind 能 might make more sense to me. 「希望我們很快能夠再見」
1. 口 is no longer used solely to mean "mouth" in modern literature, this function exists probably only in ancient Chinese now. Also 口 isn't used in daily conversations, at least not in mandarin. Not even in formal situations. You can use 嘴巴，or 嘴 (the most used one) anytime. When do you use 口？ it usually appears with another character and mean a LOT of other means that might have nothing to do with a mouth like 借口 (an excuse)，胸口 (chest/breast)，胃口 (appetite)，But it can still mean something relevant to a mouth, like 口音 (accent), 洞口 (the opening of a cave)，出口 (the exit, the sign that's everywhere)，口腔 (the inside of the mouth, you'll encounter this in hospitals or technical books)，口部 (it means your mouth, but it's more like a technical word.). etc. etc. etc. etc. etc. (Chinese here)