How to use "是否"

是否 is translated into "whether or not; whether; if ", which is a bit misleading. It is probably closest to "whether or not", but it's far from “如果” (if). 

是否 = adj 不 adj/verb 不 verb/verb 没 verb

是 means affirmative and 否 means negative in ancient Chinese. The best way to understand 是否 is to know that it has the same grammatical function as the question patterns: adj 不 adj/verb 不 verb/verb 没 verb.

你忙不忙? = 你是否很忙?     (If the adjective is only one character, we need an adverb here, such as 很,非常,有点儿)

Are you busy or not?

这样说正确不正确? = 这样说是否正确? (If the adjective is more than one character, we don't have to add adverbs)

Is it correct to say it in this way or not?

你是不是美国人?= 你是否是美国人?

Are you American or not?

你昨天学没学汉语? = 你昨天是否学汉语了?(了 is required if it's in the past)

Did you learn Chinese yesterday or not?

我不知道他明天会不会来。 = 我不知道他明天是否会来。

I don't know whether or not he will come tomorrow.

不管周末下不下雨,我都要去爬山。 = 不管周末是否下雨,我都要去爬山。

Whether it rains or not in the weekend, I want to go climbing. 

"是否" can't refer to assumptions, we have to use "如果" or “要是……(的话)”; vice verse, "如果" or “要是……(的话)” are not able to refer to two opposite situations. 

If you can come to the party tomorrow, I would be very happy.

明天你是否可以来参加聚会,我会非常高兴。 (F)

明天你如果可以来参加聚会,我会非常高兴。  (T)

I am not sure whether or not he will come to the party tomorrow.

我不知道他明天如果会来参加聚会。          (F)

我不知道他明天是否会来参加聚会。           (T)


So that's all there is to know about " 是否". 你们是否明白了?(Do you understand or not?)