 A further way in which participatory intentions of different individuals are related stems from how they might be formed, modified, or set aside. For example, Gilbert holds that shared activity gets started only when each individual openly expresses a readiness to be jointly committed in a certain way with  others.[21]  She adds that rescinding or significantly modifying the resulting intention, as well as releasing any individual from participation, would also require concurrence on everyone’s part. It’s not clear that Gilbert herself would want to talk of this “concurrence condition” in terms of relating intention or intention-like attitudes in different participants. But, given that whether I concur with how you propose to modify your intentions will depend in part on my intentions, it is natural to take Gilbert’s conditions as imposing dynamic constraints on how the participatory intentions of different individual are related to one another. Of course, Gilbert’s conditions might be too strong. For example, the concurrence criterion does not permit one to withdraw unilaterally from shared  activity.[22]  Some may find this implausible. But relaxing Gilbert’s conditions would naturally result in another perhaps weaker set of dynamic constraints, and not in their complete absence. For example, recall that intentions are defeasible: they can be revised or dropped if changing circumstances warrant it. Now, we might imagine that each participant in shared activity might have the authority unilaterally to revise or defeat the intention in light of those changing circumstances, whereupon other participants would have to abide by the change unless, of course, they think that some mistake has been made (Roth 2004).