Quick Answers Fail

Is The Problem of Joint Action really a problem? Not if there is a quick answer. In this section we consider three potential quick answers.

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What distinguishes doing something jointly with another person from acting in parallel with them but merely side by side?

We consider three quick answers:

1. a joint action is an action with two or more agents
2. a joint action is an event with two or more agents^[1]
3. the Simple Theory of Joint Action

None of these answers appears to be correct (although, as always, none of the considerations offered are decisive).

Aims. In rejecting the quick answers we aim to better understand the Problem of Joint Action and why it is difficult to answer, thereby showing that it really is a problem.

Background: Paradigm Cases

What are some supposedly paradigm cases of joint action?

Cases offered as paradigms in philosophy include two people painting a house together (Bratman, 1992), lifting a heavy sofa together (Velleman, 1997), preparing a hollandaise sauce together (Searle, 1990), going to Chicago together (Kutz, 2000), and walking together (Gilbert, 1990).

In developmental psychology, supposedly paradigm cases of joint action include two people tidying up the toys together (Behne, Carpenter, & Tomasello, 2005), cooperatively pulling handles in sequence to make a dog-puppet sing (Brownell, Ramani, & Zerwas, 2006), and bouncing a block on a large trampoline together (Tomasello & Carpenter, 2007).

Other supposedly paradigm cases from research in cognitive psychology include two people lifting a two-handled basket (Knoblich & Sebanz, 2008), putting a stick through a ring (Ramenzoni, Davis, Riley, Shockley, & Baker, 2011), and swinging their legs in phase (Schmidt & Richardson, 2008, p. 284).

We should not assume that these are all paradigm cases.

Nor should we assume, without argument, that there is a single phenomenon of which all these are paradigm cases.

Are joint actions simply actions with two or more agents?

The short answer is no, because:

1. primitive actions (whether bodily movements or tryings) are ‘all the actions there are’ (Davidson, 1971, p. 59); and

2. in many paradigm cases of joint action (see above) there are clearly no primitive actions with multiple agents.

In painting a house, walking together or lifting a two-handled basket we each move only our own bodies directly.

The notion of a joint action as an action with two or more agents is therefore too narrow relative to our aim of theorising about a range of cases taken to be paradigmatic joint actions. (This is not to say that no actions have two or more agents; see Blomberg, 2011.)

Against this consideration, you may object that

Are joint actions simply events with two or more agents?

To illustrate, suppose two hunters each attack a deer. Neither attack was individually fatal but together they were deadly. In this case the hunters are agents of the killing of the deer, so the event counts as a joint action on Ludwig’s proposal.

To fully understand Ludwig’s proposal we need to understand what it is for an individual to be among the agents of an arbitrary event and not just an action. This can be done in terms of a notion of grounding which I adapt from a discussion of action by Pietroski (1998).

Pietroski identified a simple and elegant way of generalising from the idea that an individual can be the agent of an action to the idea that an individual can be the agent of a larger event. (His account does require a minor correction, but this is not relevant here.) This can be generalised to allow for any number of agents.

Let us stipulate that events D₁, ... D_n ground E, if: D₁, ... D_n and E occur; D₁, ... D_n are each (perhaps improper) parts of E; and every event that is a proper part of E but does not overlap D₁, ... D_n is caused by some or all of D₁, ... D_n.

Then let us say that for an individual to be among the agents of an event is for there to be actions A₁, ... A_n which ground this event, where the individual is an agent of some (one or more) of these actions.

To illustrate, consider the hunters again. Let the episode be an event comprising only the hunter’s actions, the deer’s death and the events causally linking these. Since, for each hunter, there is a set of events including this hunter’s attacking which ground the episode, we can conclude that the episode is a joint action on Ludwig’s proposed definition.

This definition is too broad. To see why, consider two ways of elaborating the story about the hunters. In one they are best friends who have set out together with the aim of killing this deer, and they are exhibiting many features associated with paradigm cases of joint action. In the other elaboration, the hunters are bitter rivals completely unaware of each other’s presence. In fact, were either to have suspected the other was present, she would have abandoned the deer in order to target her rival. In both elaborations, Ludwig’s proposal entails that the episode is a joint action. But whereas the ‘best friends’ elaboration resembles paradigm cases of joint action, the bitter rivals are merely acting in parallel.

Is the Simple Theory of Joint Action True?

Imagine two sisters who, getting off an aeroplane, tacitly agree to exact revenge on the unruly mob of drunken hens behind them by positioning themselves so as to block the aisle together. This is a joint action.

Meanwhile on another plane, two strangers happen to be so configured that they are collectively blocking the aisle. The first passenger correctly anticipates that the other passenger, who is a complete stranger, will not be moving from her current position for some time. This creates an opportunity for the first passenger: she intends that they, she and the stranger, block the aisle together. And, as it happens, the second passenger’s thoughts mirror the first’s. So the condition imposed by the Simple Theory of Joint Action is met: each passenger is acting on her intention that they, the two passengers, block the aisle together and these intentions are appropriately related to their actions.

But the contrast between the cases of the strangers and the sisters exacting revenge suggests that the stranges passengers are not taking part in a joint action.

Apparently, then, the Simple Theory of Joint Action is false because the condition is implies is sufficient for joint action can be met even where there is no joint action at all.

Further Reading

There are interesting discussions which may motivate the view that we do not need a theory of shared intention to solve The Problem of Joint Action in Baier (1997), Chant (2007), Petersson (2007), and Longworth (2019, p. 13ff).

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