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\title {Origins of Mind: Lecture Notes \\ Shared Agency Involves}

\maketitle

# Changing Perspective

\def \ititle {Origins of Mind}
\def \isubtitle {Shared Agency Involves}

\

\begin{center}
{\Large
\textbf{\ititle}: \isubtitle
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\iemail %
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Shared agency is a familiar feature of everyday life.
We move tables together, share smiles, we cry together, we paint houses together, ... oh, and we kiss.
In doing these things we are, I suppose, manifesting shared agency of some kind or other.
Shared agency is manifested in paradigm cases where two agents move a table together, share a smile or cry together, paint a house together, change a nappy together or kiss.
My overall question is:
\textbf{Question}
Which kinds of planning mechanisms enable agents to coordinate their actions and what (if anything) do these mechanisms tell us about the nature of shared agency?
But I want to start by trying to get a firmer fix on the notion of shared agency by contrasting actions involving shared agency with actions that involve parallel but merely individual agency ...%
\footnote{
Compare \citet[][p.\ 150]{Bratman:2009lv} and
\citet{roth_shared_agency}, §1.
}
(Here, by the way, I'm going to stipulate that a joint action is a manifestation of shared agency; so, in my terms, there's no joint action without shared agency.)

\section{Shared vs Parallel but Merely Individual Agency}

\section{Shared vs Parallel but Merely Individual Agency}
Joint action is a familiar feature of everyday life.
Two sisters cycling to school together are engaged in a joint action,
whereas two strangers who happened to be cycling the same route side-by-side would not be (compare \citealp{gilbert_walking_1990}).
Two sisters cycling to school together exercise shared agency whereas two strangers who happened to be cycling the same route side-by-side do not (compare \citealp{gilbert_walking_1990}).
Similarly, when members of a flash mob in the Central Cafe respond to a pre-arranged cue by noisily opening their newspapers, they perform a joint action.
But when someone not part of the mob just happens to noisily open her newspaper in response to the same cue, her action is not part of any joint action.%
\footnote{
See \citet{Searle:1990em}; in his example park visitors simultaneously run to a shelter, in once case as part of dancing together and in another case because of a storm.
Compare \citet{Pears:1971fk} who uses contrast cases to argue that whether something is an ordinary, individual action depends on its antecedents.
}
When members of a flash mob respond to a pre-arranged cue by noisily opening their newspapers, they exercise shared agency. But when others happen to noisily open their newspapers in response to the same cue, they do not \citep[compare][]{Searle:1990em}.
These and other contrast cases invite the question,
\textbf{What distinguishes joint actions from parallel but individual action?}

\textbf{Question} What distinguishes exercises of shared agency from parallel exercises of merely individual agency?
The first contrast case shows that the difference can’t be just a matter of coordination because people who merely happen to be cycling side-by-side also need to coordinate their actions in order to avoid colliding.
Note also that in both cases each individual's cycling is intentional, so our intentionally cycling together cannot be only a matter of our each intentionally cycling.
The second contrast case shows that the difference can’t just be that the resulting actions have a common effect because merely parallel actions can have common effects too.

At this point it is natural to appeal to intention.
If we are performing actions of some type phi,
then perhaps for our doing this to be a joint action is just for us to be doing this
because we each intend that we, you and I, phi together.
So in the case of the cycling sisters, each would intend that they, the two sisters cycle to school together.
I'm going to come back to this idea so it's helpful to give it a label.
Let's call it the Simple Account of intentional joint action.

each sister intends that
they, the sisters, cycle to school together?

Does the appeal to togetherness make this circular? Not as long as we understand 'together' only in the sense in which the three legs of a tripod support the flask \emph{together}.
So we have to understand the intention as concerning an event type that could be a joint action but might also involve merely parallel actions.

\textbf{Simple Account}
Intentional joint action occurs when there is an act-type, φ, such that each of several agents intends that they, these agents, φ.
This certainly distinguishes the cases on your left from those on your right.
But we can see that the Simple Account is too simple as it stands by adapting an example from Gilbert and Bratman ...
Contrast two friends walking together in the ordinary way,
which is a paradigm case of collective agency,
with a situation where two gangsters walk together but each is forcing the other.
It works like this: Gangster 1 pulls a gun on Gangster 2 and says: “let’s walk”
But Gangster 2 does the same thing to Gangster 1 simultaneously.
This is walking together in the Tarrantino sense,
and clearly not a case of joint action.
At least it’s not joint action unless the central event of of Reservoir Dogs is also a case of joint action.
Since in this case there is something which all the agents involved intend, it seems that our being involved in a joint action can't be a matter only of there being something such that we each intend that we do it together.

\section{Bratman on Interconnected Planning}

\section{Bratman on Interconnected Planning}

shared intentional agency consists, at bottom, in interconnected planning agency of the participants.’

(Bratman 2011, p. 11)

Facts about your plans feature in my plans & conversely.

Bratman’s brilliant idea for avoiding this sort of problem is to suggest that we don’t just each intend the action but rather we each intend to act by way of the other's intentions.
We can put this by saying that our intentions must interlock: mine specify yours and yours mind.
Now this appeal to interlocking intentions enables Bratman to avoid counterexamples like the Tarantino walkers; if I intend that we walk by way of your intention that we walk, I suppose can't rationally also point a gun at you and coerce you to walk.

‘each agent does not just intend that the group perform the […] joint action.

‘Rather, each agent intends as well that the group perform this joint action in accordance with subplans (of the intentions in favor of the joint action) that mesh’

(Bratman 1992: 332)

So far all we've seen is that appeal to interlocking intentions provides *one way* of avoiding counterexamples like the Tarantino walkers.
But Bratman goes further. He suggests that shared agency 'consists at bottom' in interlocking planning agency.
Here, interconnected planning is planning where facts about your plans feature in my plans & conversely.
On Bratman's view, interlocking planning is necessary for shared agency, and it is a necessary part of some sufficient conditions for shared agency.
Note that this results in an austere view about shared agency ... austere wrt planning systems and wrt the kinds of agents that can exercise shared agency
If sharing a smile involves exercising shared agency, and if human infants in their first year of life are incapable of representing others’ plans and making plans about plans, then Bratman’s view entails that it is impossible to share a smile with an infant.
Now some suggest that Bratman is right about one form of shared agency, but that there are other, less demanding forms of shared agency (Tollefsen, Pacherie).
I used to think this too, but recently I’ve come to the view that Bratman is wrong about shared agency.
In this talk I’ll argue that there is no form of shared agency that consists at bottom in interconnected planning. Interconnected planning is not sufficient for shared agency.
each agent does not just intend that the group perform the […] joint action. Rather, each agent intends as well that the group perform this joint action in accordance with subplans (of the intentions in favor of the joint action) that mesh' \citep[p.\ 332]{Bratman:1992mi}.
Our plans are \emph{interconnected} just if facts about your plans feature in mine and conversely.
‘shared intentional [i.e.\ collective] agency consists, at bottom, in interconnected planning agency of the participants’ \citep{Bratman:2011fk}.

shared intentional agency consists, at bottom, in interconnected planning agency of the participants.’

(Bratman 2011, p. 11)

Facts about your plans feature in my plans & conversely.

parallel planning

You plan our actions, yours and mine, and I plan our actions too

Having done that, I'll also argue that a different form of planning, parallel planning, is sufficient for shared agency.
In parallel planning, you plan our actions, yours and mine, and I plan our actions too.
So my talk has two parts.

first part: Interconnected planning is not sufficient ...

second part: ... and parallel planning is sufficient for shared agency.

But here I’m getting far ahead of myself, and at this stage the very idea of parallel planning may well seem incoherent.
So let me put parallel planning aside for a moment.
The first task is to show why Bratman's view is wrong and why interconnected planning is not sufficient for shared agency.
One nice feature of Bratman’s view is that he can cash out the idea about interconnected planning in a very clear way.
Here’s how it goes.
Shared agency involves shared intention, and for us to have a shared intention that we J, it is sufficient that ...
So to show that interconnected planning is not sufficient for shared agency, it suffices to show that these conditions can be met without the agents in question having a shared intention that they J.
\emph{Bratman’s claim}. For you and I to have a collective/shared intention that we J it is sufficient that: (1)(a) I intend that we J and (b) you intend that we J; (2) I intend that we J in accordance with and because of la, lb, and meshing subplans of la and lb; you intend that we J in accordance with and because of la, lb, and meshing subplans of la and lb; (3) 1 and 2 are common knowledge between us' \citep[View 4]{Bratman:1993je}

shared intentional agency consists, at bottom, in interconnected planning agency of the participants.’

(Bratman 2011, p. 11)

Facts about your plans feature in my plans & conversely.

We have a shared intention that we J if

‘1. (a) I intend that we J and (b) you intend that we J

‘2. I intend that we J in accordance with and because of la, lb, and meshing subplans of la and lb; you intend [likewise] …

‘3. 1 and 2 are common knowledge between us’

(Bratman 1993: View 4)

Needed to avoid circularity ... so this has to be neutral wrt shared intentionality.
It's also important, for Bratman's account and for my purposes, that I can intend *unilaterally* that we J. That is, I can intend that we J without depending on your also intending that we J.
Use ‘blocking the aisle’ as an example an action that can, but needn’t be, an exercise of shared agency. There are two people ahead of us on the train. They are blocking the aisle. We don’t know whether they are doing this intentionally or accidentally, nor whether their doing this is an exercise of shared agency or not. But still we can decide, in a sufficiently perverse mood, we shall do what they are doing. We can decide this without knowing whether what they are doing is an exercise of shared agency or not. The thing we are deciding to perform is an act-type that is neutral with respect to shared intentionality. Now this has a consequence that will be important for me. It means that one of us can intend that we J unilaterally, that is, irrespective of what the other intends. Suppose I know that you are going to stand where you are standing whatever I or anyone else does. You are rooted to the spot. Then I can decided that we will block the aisle, and I can decide this unilaterally because I know that you will do your part despite having no such intention.
This is the key to the possibility of UNSHARED INTENTION.

\section{Counterexample to Bratman}

\section{Counterexample to Bratman}
The conditions for unshared intention are just like those for shared intention except that they concern two distinct activities, J1 and J2.
So for you and I to have an unshared intention that we , ...
If it is possible for Bratman's sufficient conditions for shared intention to be met without relevant irrationality or ignorance, then it is likewise possible for these conditions on unshared intention to be met.
\begin{minipage}{\columnwidth}
We have an \emph{unshared intention} that we <J$_1$, J$_2$> where J$_1$$\neq$J$_2$ just if:
\begin{enumerate}[label=({\arabic*$^\prime$}),itemsep=0pt,topsep=0pt]
\item (a) I intend that we J$_1$ and (b) you intend that we J$_2$
\item I intend that we J$_1$ in accordance with and because of la, lb, and meshing subplans of la and lb; you intend that we J$_2$ ...
\item 1 and 2 are common knowledge between us.
\end{enumerate}
\end{minipage}
Our individual subplans concerning our <J$_1$, J$_2$>-ing \emph{mesh} just in case there is some way I could J$_1$ and you could J$_2$ that would not violate either of our subplans but would, rather, involve the successful execution of those subplans.

We have an unshared intention that we <J1, J2> iff

‘1. (a) I intend that we J1 and (b) you intend that we J2

‘2. I intend that we J1in accordance with and because of la, lb, and meshing subplans of la and lb; you intend [likewise] …

‘3. 1 and 2 are common knowledge between us’

We have a shared intention that we J if

‘1. (a) I intend that we J and (b) you intend that we J

‘2. I intend that we J in accordance with and because of la, lb, and meshing subplans of la and lb; you intend [likewise] …

‘3. 1 and 2 are common knowledge between us’

(Bratman 1993: View 4)

Here is an example of two people who have an unshared intention.
Ayesha and Ahmed. They can each tilt the table, but only along one axis.
(Note that Ayesha can unilaterally intend that they, Ayesha and Ahmed, make the ball hit the red square.)

If you think Ayesha and Ahmed are having a bad hair day, you should see Beatrice and Baldric ...
Now explain that Ayesha and Ahmed have an unshared intention, but Beatrice and Baldric have a shared intention.
So they do have interlocking plans.
This is a bit delicate. I am supposing that Beatrice and Baldric are each making use of the fact that Beatrice intends J1 and of the fact that Baldric intends that J2, but that they are neglecting to make any use of the fact that J1=J2.
So the only difference is that Beatrice and Baldric happen to have same task, whereas Ayesha and Ahmed have different tasks. But neither Beatrice nor Baldric makes use of the fact that they have the same task.
Beatrice does rely on the fact Baldric intends that they J1, of course; but she does not rely on the fact that what Baldric intends is what she intends.

 true? A&A make use of? Ayesha intends J1 ✓ ✓ Ahmed intends J2 ✓ ✓ J1=J2 ✗ ✗

 true? B&B make use of? Beatrice intends J1 ✓ ✓ Baldric intends J2 ✓ ✓ J1=J2 ✓ ✗

What's missing from Beatrice and Baldric's case that makes their actions not an exercise of shared agency? I think one factor is that they don't themselves conceive of their agency as in any relevant way shared, nor of their actions as joint actions. Lots of actions involve others' agency without thereby being exercises of shared agency. From Beatrice and Baldric's points of view, theirs is just such an action. From their point of view, what they are doing no more involves shared agency than do the actions of a golfer whose hole-in-one depends on the hard work of a gardener keeping the grass short and flat.
So we can add Beatrice & Baldric to the right side of our list of cases of parallel but merely individual action.
This is a case where we have interconnected planning but no shared agency.
So shared agency doesn’t consist at bottom in interconnected planning agency.
(I might mention that there are also mundane counterexamples.)

Shared Agency

Parallel but Merely Individual

Beatrice & Baldric’s making the cross hit the red square

Two sisters cycling together.

Two strangers cycling the same route side-by-side.

Members of a flash mob simultaneously open their newspapers noisily.

Onlookers simultaneously open their newspapers noisily.

So I reject Bratman's claim that shared intentional agency consists at bottom in interconnected planning.

shared intentional agency consists, at bottom, in interconnected planning agency of the participants.’

(Bratman 2011, p. 11)

Facts about your plans feature in my plans & conversely.

We have a shared intention that we J if

‘1. (a) I intend that we J and (b) you intend that we J

‘2. I intend that we J in accordance with and because of la, lb, and meshing subplans of la and lb; you intend [likewise] …

‘3. 1 and 2 are common knowledge between us’

(Bratman 1993: View 4)

\section{Parallel Planning}

\section{Parallel Planning}

Parallel Planning

What’s wrong with B&B is that they don’t conceive of their actions as an exercise of shared agency.
What we want is some way to capture the sense that agents engaged in shared agency conceive of their actions as exercises of shared agency, without of course going in a circle by appealing directly to shared agency here.
At this point it’s tempting to appeal to romantic notions of sharing, or to introduce distinctive ingredients like special modes of thought, special ontological constructs or special kinds of reasoning. I want to suggest a way of capturing the agents’ perspective without any such distinctive ingredients. This is where parallel planning comes in. Let me explain ...
A representation or plan is \emph{agent-neutral} if its content does not specify any particular agent or agents; a planning process is agent-neutral if it involves only agent-neutral representations.
Practical vs theoretical reasoning: ‘The mark of practical reasoning is that the thing wanted is \emph{at a distance} from the immediate action, and the immediate action is calculated as a way of getting or doing or securing the thing wanted’ \citep[p.\ 79]{Anscombe:1957ln}. See also \citet[p.\ 1]{millgram:2001_practical}: ‘Practical reasoning is reasoning directed towards action: figuring out what to do, as contrasted with figuring out how the facts stand.’
Some agents each \emph{individually make a plan for all the agents' actions} just if: there is an outcome; each agent individually, without discussion, communication or prior arrangement, plans for that outcome; and each agent’s plan specifies roles for herself and all the other agents.
Our plans are \emph{parallel} just if we each make a plan for all of our actions.
Two or more plans \emph{match} just if they are the same, or similar enough that the differences don't matter in the following sense. First, for a particular agent's plan, let the \emph{self part} be those steps concerning what will be the agent's own actions and let the \emph{other part} be the other steps. Now consider what would happen if, for a particular agent, the other part of her plan were as nearly identical to the self part (or parts) of the other's plan (or others' plans) as psychologically possible. If the agent's self part would not be significantly different, let us say that any differences between her plan the other's (or others') are not relevant for her. Finally, if for some plans the differences are not relevant for any of the agents, then let us say that the differences don't matter.
Suppose you and I are tasked with moving this table through that door.
In doing this, must my plan take into account facts about your intentions as well as about the weight of the table, width of the door &c?
This case has some special features: (i) there is a single most salient route for the table given our objective; (ii) there is a single most salient way of dividing up the roles between us.
I suggest that, in this situation, neither of us needs to form a plan involving the others' intentions.
The situation makes this redundant.
All we have to plan is how we should move the table through the door.
By contrast, where there is no single most salient way of dividing roles ...
... in these situations it may well be right that we need to consider each other's intentions in our planning.
but in the simplest situations
Where there is a single most salient plan and a single most salient distribution of roles,
it seems to me that our making plans concerning each other's intentions is unnecessary.
It's enough that we each plan how the table is best moved.
This is inspiration for the view that shared agency *sometimes* requires parallel and not interconnected planning ...

shared intentional agency consists, at bottom, in interconnected planning agency of the participants.’

(Bratman 2011, p. 11)

Facts about your plans feature in my plans & conversely.

parallel planning

You plan my actions as well as yours, and I do likewise.

In parallel planning, I plan all of our actions and you do the same.
I want to suggest that shared agency sometimes requires only parallel, and not interconnected planning.
Some of you are probably already thinking that the very idea of parallel planning is incoherent,
and I will face up to this objection. But first I want to offer a second illustration ...
Suppose you and I are parents about to change our baby's nappy.
This involves preparing the baby and preparing the nappy.
You're holding the baby and I'm nearest the pile of clean nappies, so there's a single most salient way of dividing the task between us.
Preparing the baby is, of course, a complex action ...
Now there are relational constraints on how the baby and nappy should be prepared; how you clean constrains and is constrained by how I prepare the clean nappy (because we don't want to get pooh on it). How do we meet these relational constraints? The fact that I have a plan for the whole thing and so do you, and the fact that these plans are identical or similar enough that the differences don't matter means that your plan for your actions is constrained by your plan for my actions, which is my plan for my actions. So thanks to our parallel planning---to the fact that we each plan the whole action---your plan for your actions is indirectly constrained by my plan for my actions; and conversely. So: in parallel planning, we meet these relational constraints not by thinking about each other's intentions but by planning each other's actions.
There's just one tiny problem. In supposing that we both plan the whole action, I'm implying, of course, that we each plan actions that are not our own. And this seems incoherent, unless perhaps we (the agents performing the action) are irrational or ignorant. It seems incoherent because the elements of plans are intentions, so in planning your action I would be intending your actions. But I can't intend your actions. What can we do?
At this point I want to step back from joint action and think about practical reasoning without joint action.
First consider a standard way of distinguishing practical reasoning from theoretical reasoning ...
\citet[p.\ 1]{millgram:2001_practical}: ‘Practical reasoning is reasoning directed towards action: figuring out what to do, as contrasted with figuring out how the facts stand.’
[*skip: comes in later] Note that in practical reasoning one has a special perspective on the actions; one illustration of this is that you ignore biases and quirks, even if these are highly reliable.

without joint action

practical reasoning concerning actions that another will eventually perform Practical reasoning can occur concerning actions that another will eventually perform.This can be useful for making predictions (example from goal ascription paper).(Or use the example of one skilled decorator predicting how another would proceed: she plans just as she would if she were going to do the job, except that the result of the planning is not an intention but a prediction (belief).)You may say that this is incoherent, but note two things ...

agent-neutral

First, the plan is agent-neutral.
It is, if you like, just a description of what could be done by an agent in her situation in order to achieve a particular goal.
It is not a specification of what she should do.

no practical attiude

Second, practical reasoning concerning another's actions does not result in a practical attitude. (A practical attitude is an intention or something like it; world-to-mind direction of fit.)
What prediction requires is that you believe, concerning the plan, that it identifies a reasonable way of achieving some goal.
So that some of your practical reasoning concerns others' actions does not entail that you have practical attitudes towards their actions.
Now you might say that this is not practical reasoning at all. But note that it is sufficient preparation for action. Suppose you find out that the electrician can't make it, so you ask the decorator to stand in as the electrician. She does not have to engage in further planning or practical reasoning; she is already poised to act. So even if you want to say, for some reason, that reasoning concerning others' actions cannot be practical, you should recognise that it shares with practical reasoning this feature: it serves to put one in a position to act.

in joint action

What happens in joint action? I want to distinguish two possibilities ...

practical reasoning concerning my actions plus predictions about yours

We can imagine a situation where I think what I should do, then predict what you will do given that I do what I plan, then update my plan, then update my predictions, then ...
When I do this, I am conceiving of your actions as merely opportunities to exploit and constraints to work around.
(This is consistent with meeting the conditions Bratman offers for shared intention.)

vs

practical reasoning concerning our actions

Alternatively, I can engage in practical reasoning concerning what we should do.
This sounds incoherent, but recal that I can also engage in practical reasoning concerning another's action for the purpose of predicting it.
And note that there is reason to think that these two different ways of reasoning about what to do might, in some cases, yield different conclusions (hi-low: don't explain).
Of course, this requires that the plan I make is agent-neutral.
And it requires that pratical reasoning doesn't invariably result in my having a practical attitude to the whole plan.
But, if that's right, what attitude could I have towards this agent-neutral plan?

Dilemma: Which attitude could one have?

If the agent-neutral plan is to result in me acting, then I need to have some sort of practical attitude towards it.
But since some of the actions it specifies are, I know, actions you will eventually perform, I can't simply intend to implement the plan.
So here I seem to face a dilemma.
[First horn: not intention]
It seems that I can't intend it in the ordinary sense because then I'd be intending its parts, and some of its parts are actions that, I know, you will eventually perform.
So, apparently, I'm blocked from intending the plan
[Second horn: not belief]
On the other hand, if I merely entertain a belief about the plan --- if, for instance, I merely believe that the plan identifies a way we could achieve some goal ---
then it's unclear how I could be acting on it at all.

open-ended intentionsTo solve this dilemma we need to appeal to some ways in which intentions can be open-ended.: whatIt's a familiar idea that intentions can be open-ended with respect to what is intended.For instance, you can intend to visit the Weinachtsmarkt without intending to do so on any particular day., and whoIt's also true that intentions can be open-ended with respect to who will act on them.Consider a couple planning some tasks at the start of the weekend: they need to buy bread, to clean the bath, ... At this point, their intention is that one or both of them will do each of these things, but there is no further specification concerning who will act. Now you might say that you can't intend something without settling who will act. But this seems wrong given that (i) the couple's attitudes are practical, and (ii) generate requirements concerning agglommeration. (Even before it's determined who will do what, I know that I'm not going to be able to spend the afternoon in the pub.)[*skip] You might also say that open-ended intentions generate pressure to filling in details. This is true, but the details are not always filled by further intentions. At some point intentions give out and we just act. The point of appealing to the table-moving example was that here there is no need for the intention to specify the agents.I want to suggest that appeal to the open-endedness of intentions will help with the dilemma I had.The problem was, what attitude could I have to another's actions?

The attitude I can have is this: with respect to the whole plan, I intend that we implement it.
And with respect to its components, I intend that you or I or we do it.
So my intentions don't specify who will do what.
But they don't need to, because this is already adqeuately specified by the fact that you're holding the baby and I'm nearest the clean nappies.
So in this case what determines who does what are the constraints, not the intentions.

shared intentional agency consists, at bottom, in interconnected planning agency of the participants.’

(Bratman 2011, p. 11)

Facts about your plans feature in my plans & conversely.

parallel planning

You plan my actions as well as yours, and I do likewise.

This is why, despite appearances, I think the notion of parallel planning is coherent. Without irrationality or ignorance, it is possible for us each to plan all of our actions, yours and mine, and to act on these plans. In doing so we achieve coordination and manifest collective intentionality not by thinking about each other's plans but, more directly, by planning each other's actions.
Let me return for a moment to the Tarantino walkers and what I was calling the Simple Account of shared intention. According to the Simple Account, we have a shared intention that we walk just if we each intend that we, you and I, walk. Now, as you may recall, earlier I noted that this seemed not sufficient because we might have and act on such intentions while forcing each other to walk at gunpoint. It is this problem that Bratman uses to invoke interconnected planning. But actually we can see that the problem can also be overcome by invoking parallel planning.
Consider the view that for us to exercise shared agency in walking together it is sufficient that: (a) we each intend that we, you and I walk; (b) we pursue these intentions by means of parallel planning (that is, we each plan all our actions and our plans match); and (c) we each end up with open-ended intentions concerning the components of our plans.
This view rules out the Tarantino walkers (who each point a gun at the other) because pursuing an intention by means parallel planning means taking a practical attitude towards each other's actions. So, if my conditions are met, your pointing a gun at me would be almost like your pointing a gun at yourself in order to force yourself to do something you intend.
One more thing about interconnected and parallel planning. Earlier I noted that interconnected planning is demanding in two respects: it's demanding with respect to which mechanisms can underpin shared agency, and with respect to which agents can exercise shared agency. By contrast, parallel planning is not demanding in these respects. In parallel planning, I don't make plans about your plans, I simply plan your actions. So it does not demand mechanisms which are capable of meta-planning, nor agents capable of understanding and thinking about others' plans. Recognising a role for parallel planning in shared agency may thus allow us to understand exercising shared agency might not presuppose deep insights into the nature of minds, and so tempt us to consider the conjecture that it is through acting together that we first come to understand other minds. But that is another talk ...
Now so far I've been arguing only that (i) the notion of parallel planning is coherent, (ii) that parallel planning enables us to coordinate our actions, and (iii) that appeal to parallel planning might be useful for explaining shared agency because it gives us a way of ruling out some counterexamples. But that doesn't, by itself, amount to showing that the notion of parallel planning can is any more useful than that of interconnected planning. For all I've said so far, it might be that both parallel and interconnected planning play a role in corrdinating actions, but neither can be used to give sufficient conditions for intentional joint action. Can I do better?

practical unity

Earlier I suggested that interconnected planning can't be what shared agency at bottom consists in because agents can have interconnected plans while thinking of each other's actions only as opportunities to exploit and constraints to work around, and so without conceiving of themselves as exercising shared agency.
Now I want to suggest that in parallel planning, we take a perspective that allows us to see our actions, yours and mine, as having a certain kind of practical unity.
Making a single plan for some actions involves treating those actions as having a kind of practical unity.
To illustrate, first consider the case of a single individual.
Imagine someone committed to keeping two or more areas of her life apart, so that she tries to plan separately for each area of her life. When concerned with planning in one area, she treats ongoing and planned actions from other areas of her life almost as if they were the actions and intentions of another agent who is temporarily acting with her body. Actions from other areas of her life feature in her current planning only as constraints to work around or opportunities to exploit. Of course, many of her predictions about her own actions are based on plans she has made when thinking about other areas of her life. But she systematically avoids conceiving of any two plans for different areas of her life as even potentially parts of a single, larger plan. So there is a kind of practical unity that she fails to conceive of the actions which make up her life as having. She never takes a planning perspective with respect to all her actions. Instead, at each time she plans for just one area of her life and takes the perspective of an outsider on the other areas of her life. %Echoing Moran, we might put the idea roughly by saying that she is constantly estranged from the actions making up one or another area of her life.
As this illustrates, the ability to conceive of all our actions as potentially parts of a single plan matters partly because it allows us to see them as having a kind of practical unity.
This applies to how you conceive of others' actions, not just your own. Earlier, in Section \ref{sec:distributed_plan} (\vpageref*{sec:distributed_plan}), I argued that you can sometimes rationally plan not only your own but also others’ actions. Therefore it is sometimes possible to take the sort of perspective on others’ actions that you would paradigmatically take on your own actions. %***thanks to Peter Fossey here I am not suggesting, of course, that you thereby conceive of others’ actions exactly as if they were your own. But nor do you conceive of the others’ actions in quite the way you would conceive of the actions of just any other agent who happened to be passing by. Rather, you conceive of these actions as on a par with your own actions insofar as they are all elements of a single plan.
With this notion of parallel planning in mind, I want to return to my counterexample to Bratman's view.
Recall Beatrice and Baldric who had interlocking plans.
Since (by stipulation) they each avoid conceiving of these plans as even potentially parts of a single larger plan, at any point in time each is taking the perspective of an outsider on either her own or the other’s actions.
To see that there really is no shared agency, contrast these two with Caitlin and Ciaran who engage in parallel neutral planning for J1 ...
Here are Caitlin and Ciaran. Each plans the other’s actions as well as her own.
So there is a sense in which they see their actions as having a kind of practical unity.
I want to take two things from this.
First, the contrast between C&C and B&B shows that B&B's case really doesn't involve shared agency.
Second, the fact that C&C do manifest shared agency also shows, by the way, that interconnected planning is not necessary for shared agency.

Shared Agency

Parallel but Merely Individual

Caitlin & Ciaran’s making the cross hit the red square

Beatrice & Baldric’s making the cross hit the red square

Two sisters cycling together.

Two strangers cycling the same route side-by-side.

Members of a flash mob simultaneously open their newspapers noisily.

Onlookers simultaneously open their newspapers noisily.

conclusion

My question was, Which kinds of planning mechanisms enable agents to coordinate their actions and what (if anything) do these mechanisms tell us about the nature of shared agency?
I've been arguing that, in addition to Bratman's notion of interconnected planning, there is another kind of planning, parallel planning which can enable us to coordinate our actions. I've also argued, by giving counterexamples, that Bratman is wrong to hold that interconnected planning is either necessary or sufficient for shared agency.
In doing this, I suggested, further, that we can give sufficient conditions for an event to involve an exercise of shared agency by invoking parallel planning.
None of this implied that there is no role for interconnected planning at all. One requirement for parallel planning is that two or more agents have matching plans. I've suggested that this matching can sometimes be achieved thanks to a combination of similarities in the agents' planning abilities and environmental constraints. But there will, of course, be many situations in which these factors are insufficient to yield non-accidentally matching plans. Perhaps, then, interconnected planning matters in part because it enables agents to non-accidentally make matching plans in some situations. On this view, then, interconnected planning is not essential for shared agency but it does dramatically extend the range of cases in which we can exercise shared agency.
Sometimes interlocking intentions and knowledge states are not enough. Sometimes no amount of forming intentions about others’ intentions and acquiring knowledge of such intentions is sufficient, all by itself, for shared intention. In some or all cases, shared agency requires changing perspective to conceive of your own and others’ actions as parts of a single plan.
This matters for understanding why many of us see shared agency as important in our lives \citep[compare][p.\ 327]{Bratman:1992mi}. In exercising ordinary, individual agency, we sometimes take a perspective that allows us to see our own temporally scattered actions as having a kind of practical unity. Relatedly, exercising shared agency sometimes involves taking a perspective that allows us to see our actions, yours and mine, as having a somewhat similar unity. It is not just that our individual plans mesh. It is that we plan almost as if you and I were one. In exercising shared agency we two are practically one.