Everyone's Making This Obvious Mistake All The Time

It's 2026. You shouldn't still be making Parfit's named first mistake in moral mathematics.

Suppose that two people take an action. Each would have taken their action even if the other hadn’t. Together, their actions save two lives. Neither person acting alone would have saved any lives. Question: how should each person think of their own action? Should they think of themselves as saving one life or two?

There are two answers that people often give: one and two. Two is the right answer. We’ve known this for decades. There are decisive arguments for it. Parfit settled the dispute in 1984.

And yet people are still making this mistake. For example, here’s Leif “befuddled by stipulative definitions” Wenar:

But let’s picture that person you’ve supposedly rescued from death in MacAskill’s account—say it’s a young Malawian boy. Do you really deserve all the credit for “saving his life”? Didn’t the people who first developed the bed nets also “make a difference” in preventing his malaria? More importantly, what about his mother? She chose to trust the aid workers and use the net they handed to her, which not all parents do.

Wenar goes on to chide MacAskill for his supposed philosophical incompetence, before making a basic error that has been known about by philosophers since before I was born. Not a great look. Specifically, the view Wenar endorses is called the “share of the total view.”¹ On this view, you should analyze the impacts of your actions by dividing the total impact by the number of people who acted to produce that impact. If ten people collectively save ten lives, each only gets credit for saving one life. There might be more nuanced ways of doing this, but the basic idea is that you’re supposed to divide up credit for the impact across those who acted to produce the impact.

Contrast that with the correct view called the counterfactual view. On this view, when deciding between two actions, you should look at what happens if you take each one. When seeing how good it is for you to take an action, you should look at which morally important things in the world will be different if you take the action vs if you don’t. In the earlier case, each action is counterfactually responsible for two lives saved. Each person gets credit for saving two lives.

Here’s an easy way to see that the share of the total view is wrong. Imagine that there are two actions. You can only take one:

1. You get someone to tell his friend to pull three children out of ponds. His friend does it. Three lives are saved.

2. You buy a rope (from a vending machine, not a person) which you then use to pull two children out of ponds.

Which action is better? The obvious answer is the first one. Yet using Wenar’s logic, you should take the second one. After all, if you do the second, you get full credit for saving two lives. With the first, you only get credit for saving one third of three lives—so only one life total.

You’ll note an interesting result of the counterfactual view: the total credit awarded by multiple people taking an action can be greater than the benefit of the action. Three people each get full credit for saving three lives, even though only three total lives were saved, not nine. That is because they all took an action that was counterfactually responsible for saving three lives.

Or, to put it another way, they each took an action that if they hadn’t taken it would have led to three additional deaths. This sounds a bit weird at first, but it makes sense when you think about it. There’s no reason that the counterfactual credit coming from a sequence of acts has to equal the total benefit coming from the sequence of acts.

If multiple people are each counterfactually responsible for some effect being brought about, then total counterfactual impacts from each of their acts exceeds the good brought about. If there’s a three-judge panel in a debate round, and two of the judges vote for me, there are three people each counterfactually responsible for my victory: me and both of the judges who voted for me.

Applying this to MacAskill’s case, if you make a charitable donation, you are counterfactually responsible for saving a whole life. So are various other people. That is because all of you took an action which, had it not been taken, would have left one extra person dead.

Counterexamples to the share of the total view abound. Here’s a famous one from Parfit:

The Second Rescue Mission. As before, the lives of a hundred people are in danger. These people can be saved if I and three other people join in a rescue mission. We four are the only people who could join this mission. If any of us fails to join, all of the hundred people will die. If I fail to join, I could go elsewhere and save, single-handedly, fifty other lives.

If you divide the credit by the number of people acting, then it’s better not to join. But clearly, this is wrong. So the share of the total view must be wrong too!

By the way, the things I’m saying here are standard. I don’t know of any papers defending the share of the total view after Parfit argued against it. This is a nice example to illustrate that we do sometimes learn things in philosophy. We don’t just rehash the same debates over and over again. Sometimes, Parfit decisively shows what’s what.

Here’s an objection you might have. Suppose that there are four people. They each have an option like in the second rescue mission. So they can all go out and join the rescue mission, saving 100 lives, or they can save fifty lives on their own. If they each get credit for saving 100 lives by joining the rescue mission, then wouldn’t it be better for them to join it? And if they do that, then they save only 100 lives, rather than 200 lives. So doesn’t the counterfactual view get the wrong answer?

No!

You have to actually consider the counterfactuals. When you do this carefully, every single apparent counterexample dissolves. If any don’t join the rescue mission, then presumably the others wouldn’t either. So then the first person by not joining the rescue mission is counterfactually responsible for saving 200 lives, rather than 100 if they join. So not joining counterfactually saves an extra 100 lives.

That’s assuming that the other people would have joined the rescue mission if the first person hadn’t. What if that assumption is wrong? What if the other people wouldn’t have joined even if the first person had? Well then, even if they join, the mission still fails. So then 150 lives get saved rather than 200. Still, the view recommends not joining.

The only way the view recommends joining the rescue mission is if everyone else will join whatever you do. That way, you joining leads to 200 people being saved instead of 100. But that verdict is correct! So when you think clearly about what the counterfactual is, any apparent counterexample dissolves.

When thought about this way, the view is pretty obviously correct. When deciding between two actions, you should consider which action it would be better for you to take. You should just look at which morally relevant things will happen if you take each action, rather than arbitrarily splitting credit. You simply analyze the actual effects of your taking one action over another.

The share of the total view has other bizarre implications. It implies that credit is shared with other people, but not with non-people. So imagine two actions:

1. You pay $100 to a person who delivers medicine that saves someone’s life.

2. You pay $100 to a robot who delivers medicine that saves someone’s life.

The share of the total view treats these very differently. It implies that the second one is twice as good, because credit isn’t shared with another person. But shouldn’t these be treated the same? When taking an action that benefits someone, why the hell does it matter if the other entity in the loop is a person vs a robot? This just seems obviously irrelevant. And there are weird intermediate cases—what if it was an octopus or a baby? Any line drawn seems ridiculously arbitrary and not like the kind of thing that could feature in the fundamental rules of normativity.

So the share of the total view is simply wrong. The counterfactual view is correct. This is settled. Criticizing EAs for philosophical errors is a perfectly respectable endeavor—I’ve been known to do it myself. But you shouldn’t do it while making basic errors. And if you’re a philosophy professor who claims that “no competent philosopher” could have written a sentence providing such exotic oddities as stipulative definitions—even claiming “their flesh would have melted off and the bones dissolved before their fingers hit the keyboard”—you’re without excuse. Don’t conjoin snark and incompetence. Or, in the words of Leif Wenar:

The crucial-but-absent Socratic meta-question is, ‘Do I know enough about what I’m talking about to make recommendations that will be high stakes for other people’s lives?’

1. Technically it’s ambiguous between the share of the total view and the revised share of the total view.