Hi! Thanks for this question: First of all, once you have introduced the word "would," which is a modal verb, and also the past form of "will," you are talking about possibilities/impossibilities, abilities/inabilities, asking for and giving permissions, invitations, suggestions, and a whole lot more that we cannot go through here. Usually, the tenses used are determined by the condition. In your case, you are asking a Conditional question. How do I know, because it has an IF clause: 1. Would you be surprised if I arrived yesterday without letting you know beforehand? Yesterday is in the past tense so this is incorrect. However, "Would you be surprised to know that I had planned to arrive without letting you know," would be correct. :) This is not conditional. 2. Would you be surprised if I had arrived yesterday without letting you know beforhand? This is also incorrect. Reason: See #3. 3. Would you have been surprised if I had arrived yesterday without letting you know beforehand? This is correct. Reason: This is the Third Conditional, which you may have learned in English Grammar. Some people call it the Type 3 Conditional. It refers to an impossible condition and improbable result, because the action is in the past. So in your example, there is no way to know whether "you" would have been surprised, because the condition refers to "yesterday," which is in the past. When you use the Third Conditional, the order usually follows this pattern: would+have+past participle (This is called the perfect conditional tense). And the "IF" clause is past perfect. Does that make sense? I hope I was able to assist you? Feel free to take lessons with me where I can teach you the most common modal verbs including: would, could, should, must, might, and may. I also go through Zero Conditional, First Conditional, Second Conditional and Third Conditional. When do you use them and how do you use them? I can help. Looking forward to seeing you.. Kind regards, -Joan

These sentences are all grammatically correct. However, I would choose 1 because it is simplest.