How to ask a professor to join a project in a way that leaves him a "graceful out"? This is a follow up question to a previous question I have asked about co advising :  professor will agree to be my thesis advisor but only if I can find a co-advisor  . After sitting in on this professors lab meetings I would like to work on two projects that he is getting off the ground in collaboration with another professors lab. How can I ask him in a way that gives him a graceful out even though he agreed to co-advise on my master's thesis? I would really like to work with him since I am really interested in his research, but I do not want to end up trapping either of us in an advising relationship that would be bad for both of us in the event he was just trying to be nice when he agreed to be co-advisor on my master's thesis.
I do not want to end up trapping either of us in an advising relationship that would be bad for both of us in the event he was just trying to be nice when he agreed to be co-advisor on my master's thesis.


Give him some credit and don't assume he would agree to a bad advising relationship just to be "nice."

Ask him directly. If he wants to say "no," there are any number of ways in which he can say it.