What would be the correct use of will & would in these sentences?
1) What will happen if I say to my boss that I will not come tomorrow?
2) What will happen if I would say to my boss that I will not come tomorrow?
3) What will happen if I will say to my boss that I will not come tomorrow?
4) What would happen if I would say to my boss that I will not come tomorrow?
There are four sentences which one should I use and in which situation?
I think there's an implied meaning in using "will" vs. "would" in hypotheticals. In your first example, would and will are both correct. Will, I believe implies a higher level of expected certainty.
By that I mean, if you ask "what will happen" you're expecting the reader to infer that the answerer knows what will happen. If you ask, "what would happen" then the reader will likely infer that the answerer is making an educated guess as to what the result will be.
The following 3 sentences don't appear to be asking what you intend to ask.
The second example means, "what will happen if I am the kind of person who would actually say to my boss that I'm not coming into work tomorrow?"
The third means, "what will happen if I will say to my boss . . .?" This is a great example of how will and would have different probability assertions. The answer to this question is "you will say to your boss that you will not come tomorrow."
The fourth is just like the second except that there's an implied speculation.
Revision: After working through some of your questions in the comments, I believe I realize the problem you're having.
It appears you're looking at the future condition and expecting to put the verb in the future tense. Id est, "I will say." I believe these are called conditional sentences, specifically future conditional sentences.
There are two general forms in English:
If/When - Future Condition - Simple Present Result
If/When - Simple Present Condition - Future Result
So, your question is technically, "If I say to my boss today that I'm not coming in tomorrow, what will happen?" In English, we can arrange this question to be, "What will happen tomorrow if I say to my boss today that I'm not coming in?"
If you were to ask, "what will happen if I will say to my boss that I'm not coming to work," you could rearrange that to be "If I will say to my boss that I'm not coming to work, what will happen." I think that's how other posters have read it (and that's how I read it) and that's why it sounds confusing.
http://en.wikipedia.org/wiki/Conditional_sentence http://www.englishpage.com/conditional/futureconditional.html
Or, Google "Future Real Conditionals."
As a rule of thumb, use "would" when you are talking about hypothetical situations, and "will" when you are referring to definite possibilities.
In your examples, you are mixing the two. Number 1 is the best choice, because the hypothetical is at the beginning of the sentence (i.e., "What will" or "What would"), not the highlighted portion (e.g., "I say"). In choices 2, 3, and 4, you are mixing a second hypothetical/possibility into the sentence, which simply adds confusion.
So, if you intend to actually say this to your boss, use will:
What will happen if I say to my boss that I will not come tomorrow?
If you are merely stating a hypothetical ("What if..."), then use would:
What would happen if I said to my boss that I will not come tomorrow?
(As an aside: Use "come" if you are at the location you are referring to. Use "go" if you are not.)
I agree with D. Patrick's points, but I don't think any of the alternatives are correct. I think it should be:
What would happen if I said to my boss that I will not come tomorrow?
The phrase "I say to my boss that I will not come tomorrow" is actually in the subjunctive case, because it's a hypothetical. In English you can signify that by using the past tense. You could also use the proper subjunctive case, which sounds more formal, but also more correct:
What would happen if I were to say to my boss that I will not come tomorrow?
Number 1 is the only sentence that approaches idiomatic english. You would never put "will" or "would" between "I" and "say" in this sentence.
How you start the sentence also tends to affect the tense of the action.
If you are asking about the probable outcome of a hypothetical action, start with "what would".
If you are asking about the probable outcome of a definite (expected) action, start with "what will".
It's common to follow "what would" with the past tense:
"What would happen if I said to my boss that I will not come tomorrow?"
It's common to follow "what will" with future tense:
"What will happen if I say to my boss that I will not come tomorrow?"
It would suggest that something like it has happened in the past. Therefore, if you are asking someone who is really knowledgable about what could happen, then use would. Morover, if you are sure to ask your boss then use will, and if you aren't sure then use would.
