Reviving a Rejected Proposal -- Question on Ethical Considerations A friend of mine wrote a research proposal a few years ago. When he had 80% of it done, he pitched the idea to a colleague who joined and wrote the extra 20%. The proposal got rejected. A few years later the friend is trying to write a different proposal that has some aspects (but not content) in common with the old proposal. However, the colleague who co-wrote the old proposal will not respond to multiple emails requesting him to join the new proposal -- they probably lost interest but for some reason won't come out to say so. 

Lets assume the proposal goes ahead to submission  without involving the earlier collaborator. If the proposal were to get funded, isn't there a risk, that the earlier collaborator could turn around and claim they somehow influenced the direction of the new  proposal yet is not credited on the proposal? How in general do people move on after a joint proposal gets rejected; and some members won't be interested in joining offshoots of the old proposal. Of course in this case there is the added challenge of the earlier collaborator refusing to come out and make it clear that he is uninterested. How does one avoid the potential accusations of being unethical?
In the background that you have presented, I see only one half of the question being asked: "Will you join on this proposal?"

The clear next step is to query again with the other half, in order to make disinterest explicit, writing something along the lines of:


  Since you have not responded to my emails asking whether you would like to join this proposal, my understanding is that you are not interested.  I am intending to go ahead with this proposal, so unless I hear otherwise from you, I will assume you have no objection.


This places the question squarely with the other person.  If they respond one way or another, it resolves the question.  If they do not respond, you are free to assume that they are accepting that you submit without them.

Do, however, make certain to do due diligence to determine that the other person hasn't changed institution or email, such that your communications are not being received.  You may also want to try a phone call before giving up on contact.