I guess = I think, but I'm not absolutely sure I think = I (definitely) think (it is my opinion) I assume = based on my knowledge and experience I think/believe this I suppose = I'm not sure, but let's assume So, that means: Guess: implies some doubt or lack of conviction think: firm belief, opinion assume: Same as what you have written suppose: very close to guess, with lack of conviction, possible doubts implied. I hope this explanation was useful. If you need any help more, feel free to ask me. If you need English classes, you can book them right here: https://www.italki.com/teachers Have a nice day.