1. I had to do that = I did that because it was necessary 2. I must've done that = I'm fairly sure that I did that. Here's an example of number 2 (must've/ must have) A: 'Oh no! I've lost my cell phone!' B: Where did you lose it? A: Well, I had it in my pocket when I left my house. So I must have left it on the bus. I hope that's clear. Can you tell me something now, please? How would you translate these into French? Would you use 'J'ai dû faire' for both these situations? This will help both your English and my French. Merci.

Hello, Tim I am no teacher, but My guess is that: - I had to: means that in the past you made something for obligation, like "I felt in cold, so I had to go to the doctor". - I must have done: means that in past there is something that you did but you are not sure what, like "I must have done something special, because she likes me".

I had to do: means in the past, restrained by somebody, something or under some special circumstance, you must do something no matter whether you would or would not. I must have done: it is a prediction about you did something in the past which you can't remember but you are definitely sure.