Joint projects aren't easy to complete. Success on even a minimal joint project requires success on all lower levels of action as well. Take this exchange (8.2a.335):

Roger: now, – um doyou andyour husband haveaj- car

Nina: – haveacar?

Roger: yeah

Nina: no -

When Roger tries to ask Nina whether she and her husband have a car, she isn't sure she has heard his last phrase and queries it, “Have a car?” Only when that is cleared up does she take up his question with “No.” For success on their joint project, Roger and Nina need success in attending to, hearing, and understanding each other. How do they reach that success? In Chapter 7, we saw how two people, in pursuing a joint project, arrive at a joint construal of what the speaker is to be taken to mean. In this chapter, we look more closely at what else it takes to assure success.

The hypothesis is that people try to ground what they do together. To ground a thing, in my terminology, is to establish it as part of common ground well enough for current purposes (Clark and Brennan, 1991; Clark and Schaefer, 1989; Clark and Wilkes-Gibbs, 1986). On this hypothesis, grounding should occur at all levels of communication. Recall the ladder of joint actions from Chapter 5:

To succeed in their joint projects (level 4), A and B need to ground what A is to be taken to mean for B (level 3), and to do that, they need to ground what A is presenting to B (level 2), and to do that, they need to ground what behavior A is executing for B (level 1).