we dont use 否 structure in china and i recommend you that its better for you not to care about 否

The short answer is YES. I think it largely depends on the way you say it. To me, 能否 sounds a tad formal. Like others pointed out, 否 is an ancient Chinese word, it's very archaic, sometimes in daily conversations, it might sound a bit weird even for words like 否認(deny), 否定(negative). If I'm using this word verbally, it gives a very serious tone. Normally, I'd avoid. If written, the only times I might use this word is in Cantonese, e.g.: 可否/能否寄到英國? (Can you ship it to the UK?). Cantonese still uses a lot of archaic words, e.g.: verb 行(archaic) instead of 走 (walk), verb 食(archaic) instead of 吃 (eat), verb 飲(archaic) instead of 喝 (drink). By contrast, 能不能 sounds a lot softer than 能否 in both Mandarin and Cantonese, esp. you add a 語氣助詞 “啊” at the end of the sentence. For 是 and 可, again largely depends on the context. Nevertheless, the key word is to add a 語氣助詞 to soften your tone. 是: use in Mandarin: 是嗎? (Is it?) 是 (啊)。use in Cantonese: 是咩？是(喎)／是(噃)／是(啩) 可: 可行嗎 (is it workable)? 不可行(啊)! (unworkable/impractical) 可以嗎/Can (it/I/you)？可以! (Sure) And for 能不是, it can't be used as a replacement of 能否. Its sole usage is in the rhetorical sentence, 能不是麼／能不是嗎？For example, used when asked, 是不是這樣的(Is it like this)？Instead of giving a straight answer, 是/對的(yeah), one chooses to say 能不是嗎? That'd sound a bit mean/rude/annoyed to me. It's like how we are asked what we are doing, and we give an answer "Can't you see?" On the other hand, careful not to overuse/over-pronounce 語氣助詞, or you'd sound very 嗲 (another untranslatable Chinese word, read articles on it, scholars can't translate it, it has so many meanings, usually to describe women or kids trying to ask for favours, one of them is synonym to coquettish)

normally,if you want to express negative,such as I do "not" need it, I can "not" use this... in these cases,we use "不" you can say "不" means "not"(negative) the meaning of “否” is negative but it is usually used in a word or an expression such as "能否" “否认” “否定” here is a exp: 我不否认(something)。 in this phrase,"不" means "not" "否认" means deny, this phrase means: I dont deny(something) AND if you pose a question in this structure: can you .... or not? in chinese, we say:你能不能...... for this case,you can replace "不能" by "否"：你能不能 = 你能否 PS: "否" "之" “其” “然” these characters come from "old chinese" maybe you can try to read some "old chinese" :D it's really hard....

Hi Beth, I don't think the tone will change much when you these two structures, basically the sentences with these two structures should be followed by question marks, so i think they both should have up tone(the second tone). About when to use 否' instead of '...不....' structure, i think '能不能' is more oral, like people would use that when they chating, and '能否' is more formal, normally they just be used in articles. But both the structures are frequently used i think, you can use both of them in normal life, they just have slightly differences.