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I read somewhere that you can make tag questions by adding 是不是 to the end of the sentence. The example sentence was: 您是李老师，是不是？You are Teacher Li, aren't you?
But if the sentence doesn't have the verb 是in it, is it still correct to use 是不是 as a tag question? Example: 你认识我，是不是？
But if the sentence doesn't have the verb 是in it, is it still correct to use 是不是 as a tag question? Example: 你认识我，是不是？
Yes, even if it is a nominal predicate sentence (without verb).
Example: 明天星期五，是不是？
Besides, 是不是 can be placed at the beginning of the sentence, at the end of the sentence or between the subject and the predicate. So the following examples are all correct (see the edits below for the difference between them, if any):
Example 1: 是不是你认识我？
Example 2: 你是不是认识我？
Example 3: 你认识我是不是？
The example sentence was: 您是李老师，是不是？
That is not wrong, but please note that in the case of a "是" sentence you can also say (please see also the edit below):
您是不是李老师？
您是李老师不是？
Generally speaking, "是不是" can be used to raise questions when the speaker wants to confirm what she/he already believes.
EDIT ABOUT "您是李老师不是？"
One comment, as you can see below, surprised and puzzled me, so I contacted prof. Yang at Peking University. Please read what he said:
Giuseppe Romanazzi:
你好，老师说"是不是"正反问句的"是不是"可以加上在谓语前面，句首或者局末。我想问一下，意思完全一样吗？比如说，1) 你是不是李老师？2) 你是李老师，是不是？3) 你是李老师不是？这三个问题的意思完全一样吗？
I asked about the difference, if any, between "你是不是李老师？", "你是李老师，是不是？", and "你是李老师不是？".
杨教授:
同学你好！如果单从语义的角度看，这三个句子的意思是一样的~不过表达的 重点略有不同，第一句是普通的询问，第二句“是不是”放在句末，有强调询问的意思，第三句则更加的口语化。
Prof. Yang replied that from a semantic point of view, the meaning of the three sentences is the same, but with a slight difference. The first sentence is a general question, while in the second sentence the question is emphasized. The last sentence (the one I was more interested in), prof. Yang said, is more colloquial.
你是不是李老师？General question.
你是李老师，是不是？Emphasized the question.
你是李老师不是？More colloquial.
He didn't mention any "confrontational tone" of the last sentence. But I wanted to be 100% sure, so I went on asking:
Giuseppe Romanazzi:
谢谢老师。台湾朋友跟我说第三句"你是李老师不是？"带对抗语气，含义他不算老师。请问，在大陆也有这个意思吗？
I wrote that a friend from Taiwan told me that the sentence "你是李老师不是？" carries a confrontational tone, implying he is not a teacher. Then I added "Is it the same in the Mainland?"
杨教授:
同学你好！“你是李老师不是？”如果使用在质问的语境中，确实会比正常的语序语气更为激烈一些，但若在普通语境中使用也不一定带有对抗的意思，还是要看具体使用的环境。
Prof. Yang said that if "你是李老师不是？" is used in the context of questioning something, it will indeed be of a more intense tone than using the normal word order, but if it is used in an ordinary context, it does not necessarily have the meaning of confrontation. It still depends on the specific environment in which it is used.
EDIT ABOUT THE DIFFERENCE BETWEEN:
Example 1: 是不是你认识我？
Example 2: 你是不是认识我？
In the sentences above, 是不是 is placed at the beginning (before the subject) and in the middle (between subject and predicate) of the sentence, respectively. Is their meaning the same? Two cases must be considered.
Based on《从汉语及吴方言的正反问句看疑问和焦点的互动》(作者：祁峰). Chinese original states:
是不是老张昨天去了上海？
老张是不是昨天去了上海？
老张昨天是不是去了上海？
上例中“是不是”作为焦点算子，分别约束其后面的焦点成分“老张”、“昨天”和“上海”，而且“是不是”在句中具有浮动性，往往紧贴它的句法成分充当句子的焦点。也就是说，这里的“是不是”是针对命题内的某个成分提问的，要求对方就疑问焦点做出肯定或否定的回答，其线性位置紧邻句中的疑问焦点。
To explain the point, a little more complex example is provided. The statement that we want to transform into question is:
老张昨天去了上海。
"是不是" is used to 1) transform the statement into a question and 2) support the emphasis we give to what follows it.
是不是老张昨天去了上海？
Here "是不是" is followed by "老张". What we ask here is if it is 老张 who went to Shanghai or it was someone else.
Important: In order to focus "老张", "是不是老张" must be emphasized.
老张是不是昨天去了上海？
Here "是不是" is followed by "昨天". What we ask here is if 老张 went to Shanghai 昨天 or it was some other time.
Important: In order to focus "昨天", "是不是昨天" must be emphasized.
老张昨天是不是去了上海？
Here "是不是" is followed by "去了上海". What we ask here is if 老张 went to 上海 or somewhere else.
Important: In order to focus "上海", "是不是去了上海" must be emphasized.
Still based on《从汉语及吴方言的正反问句看疑问和焦点的互动》(作者：祁峰). Chinese original states:
至于“是不是+VP”，方梅（2005）还注意到，“是不是”不是与某个特定的疑问焦点相关，而是与整个命题相关。虽然其线性位置相对灵活，但是位置的浮动不构成疑问焦点的变化，而且“是不是”语音上弱化，语句重音总在谓语上。
这人你以前是不是见过？
这人你是不是以前见过？
这人是不是你以前见过？
上面三句中的焦点都是谓语“见过”，“是不是”虽为“重叠”这种疑问表达的语法手段，但是它本身并不能决定该正反问句中的疑问焦点。
"是不是" is not an emphasis marker by itself. The flexibility in its position in itself does not change the focus in the sentence. If no special emphasis is given, the focus is always on the predicate.
这人你以前是不是见过？
If no emphasis is given, the focus is on the predicate "见过".
这人你是不是以前见过？
If no emphasis is given, the focus is on the predicate "见过".
这人是不是你以前见过？
If no emphasis is given, the focus is on the predicate "见过".
EDIT ABOUT THE POSSIBLE MEANINGS OF:
Example 3: 你认识我是不是？(or 你认识我，是不是？)
The structure here is:
Statement + 是不是？
About the "statement" there might be three situations:
The statement is about the hearer. The statement made by the speaker is based on indirect evidence or observed phenomena, but, after all, it can only be regarded as the speaker's personal guess. Only the listener is qualified to make the final and authoritative judgment on her/his own situation.
The statement is about somebody else. This kind of statement is still the speaker's personal idea, and she/he hopes that the listener would support or confirm her/his idea.
The statement is about the speaker herself/himself who, obviously, is the one who knows better her/his own situation. The listener is often a friend or someone in a close relationship, or at least someone who is believed to share the same opinion.
Answer required?
In the first scenario, where the statement is about the listener, the "是不是" question usually has the connotation of a real question requiring an answer. A simple "是" or "不是" might be appropriate in black-and-white situations, but if the statement is only partially wrong or right, a more complex answer is normally given.
In the second and third scenarios, the main purpose of a "是不是" question is not to ask for information but for approval, and sometimes to involve the listener in the conversation or even just get her/his attention.
Politeness is showed
With a "是不是" question, the speaker seeks the approval of the listener regarding a statement made by herself/himself, putting herself/himself in a lower position than the listener. This way, she/he shows politeness and respect for the listener. This is especially true if the listeners are more than one.
P.S.: As you can see, I never fully translate in English the examples. This is done on purpose. Translations distract from learning Chinese and are often misleading. If the rule/concept is clearly explained, no translation is needed. I encourage my students to think in Chinese and avoid the bad habit to translate everything they read or listen in Chinese. Did you get the meaning? Then just remember the Chinese sentence!
You can say "You are James, aren't you?"
And you can also say "You know me, don't you?"
As "are", "know" are both verbs here.
And the same rule goes with Chinese syntax.
You can say "你是李老师，是不是？"
You can also say "你认识我，是不是？"
The only difference here is in Chinese, you can always use "是不是" as the rhetorical postfix, no matter what the real verb is in the main sentence.
But if the sentence doesn't have the verb 是 in it, is it still correct to use 是不是 as a tag question? Example: 你认识我，是不是？
Yes, you don't need to have a 是 in a statement to add 是不是 at the end of it.
"是不是" literally means "yes or no? = is it true?" It is a request for confirmation, The answer could be 是 or 不是
It could also be a rhetorical question if you already know the answer is yes, (asking 是不是 is rhetorical, you don't need an answer, you are stressing your statement)
您是個老师，是不是 = you are a teacher, is it true?/ you are a teacher, aren't you?
您姓李，是不是 = your last name is Li, is it true? / your last name is Li, isn't it?
您是個老师 and 您姓李 without the added 是不是 (confirmation request or rhetorical question) would just be plain statements
