Defining Cause

It rained today and I didn’t have an umbrella, so I got wet. Why did I get wet? What caused me to get wet?

Suppose I was in LA during a drought and it was a weird, one-off shower. You’d say that I got wet because it rained.

Suppose I was in Seattle during an especially rainy season and, uncharacteristically, I forgot my umbrella. You’d say that I got wet because I didn’t have an umbrella.

In both cases, the cause is a necessary condition. In LA and Seattle both, it is necessary (1) for it to rain and (2) for me to not have an umbrella. So a cause seems to be a necessary condition.

There are other necessary conditions in our story. For example, the sun must have risen. Without the sun, the Earth would freeze (or be blown away, it depends on why the sun was gone) so I certainly wouldn’t be getting wet. We don’t say (with seriousness) that the continued existence of the sun caused me to get wet. It’s necessary, but it’s too likely to be considered a cause.

The cause is the least likely necessary condition.

In LA, it was unlikely to rain and very likely (in a drought) that I wouldn’t have an umbrella, so the rain is the cause. In Seattle, it was very likely to rain but very unlikely I’d forget my umbrella, so the lack of umbrella is the cause.

There are times when we won’t agree on identifying a cause: (1) when we consider different sets of necessary conditions, and (2) when we don’t agree on the relative likelihood of two necessary conditions. Let’s consider some examples.

Disagreeing About Cause, Case 1
Suppose I told you that the Vogons were going to make an interstellar highway and that they were supposed to have destroyed the Earth today. At the last second someone got the date wrong and they waited until tomorrow. Now it’s very unlikely that the sun would have risen (no Earth, no sunrise) but it did, just by luck. You could credibly argue that that was the least likely necessary condition because the Vogons are very detail-oriented and are unlikely to get the date wrong. If we don’t know about the Vogons, we won’t attribute my sogginess to an alien clerical error but instead to the rain or my lack of umbrella, depending on the city. We can’t identify all of the necessary conditions, so which is least likely depends on the set of conditions we consider.

Disagreeing About Cause, Case 2
In our LA example we attribute my dampness to the weather because it was less likely than me (quite normally) not bringing an umbrella. However, my wife knows that she saw the weather forecast predicting weather and that she had told me over breakfast that I should take my umbrella. Typically I heed my much smarter spouse, so it was exceedingly unlikely that I’d forget my umbrella. And yet I did. Knowing that, my wife blames me for getting wet. You, not knowing that, blame the weather. (Someone else might ask about what distracted me from taking my umbrella, and blame that.) You and my wife have different subjective beliefs about the likelihood I’d forget my umbrella, so you disagree about the cause. Subjective probability is a central idea here. A little more context can always shift the blame.

This means that cause itself is not objective but rather is subjective, dependent on the conditions identified by the observer and the observer’s beliefs about relative likelihood.

If we can’t be sure of agreement, why bother? One reason is that when we do agree on the relative likelihood of necessary conditions, we can come to agreement about causes. Additionally, even without agreeing on all the necessary conditions to consider it’s possible to agree that something in particular is not the cause.

Suppose your loved one just died in a car accident right after you argued with them. Would you blame yourself? Probably. But suppose your loved one lost control when the brakes failed and they, distracted from the argument, didn’t regain control quickly enough to avoid the crash. Brakes fail like that very infrequently. Unfortunately, you probably argue with your loved one more often than brakes fail like that. Even if you get along very well, they’ve probably driven after arguing with you and they weren’t in an accident before. The brake failure is less likely, so you can console yourself that you didn’t cause the accident.

This might not relieve you completely. You might consider whether you contributed. There are two things to consider. First, was your argument a necessary condition? Would they have crashed without the distraction? If so, relax. But what if you think they wouldn’t have crashed without the distraction? Then secondly you might consider how much you contributed…but let’s leave that for another time.

Here are some questions the reader might consider:

  1. What does partial culpability (cause) mean using this definition of cause?
  2. Does it makes a difference whether the potential causes are human? Sometimes we’re looking for who is responsible.
  3. How can we agree “enough” about the set of necessary conditions being considered to conclude something specific is the cause?

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