What did you see in the title clip? It is likely that some of your answers to this question refer to things people did individually and others to things you people jointly with others. In commonsense thinking about action and intention, the notion that many of the things that matter most in our lives are things we do with others seems unproblematic.

But theoretically things are rather different. In developmental, cognitive and philosophical research there is a long tradition of focusing exclusively on actions with just one agent.

There is no theoretical justification for the focus on just one individual acting alone---it simply makes things easier. But to restrict attention to actions with just one agent is to exclude many of the things that matter most.

We humans are, after all, one of those species that nurture babies cooperatively. It’s not just that we care to do things with others: capacities for joint action are critical for our species’ survival.

We need, therefore, to shift focus from one individual acting along to cases in which two or more individuals act together. That is, we need to shift from individual to joint action---such as moving a log together, sharing a smile, or feeding a baby together.

And in shifting from individual to joint action, we hit a new set of integration problems.