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# [SEQ RERUN] Can Counterfactuals Be True?

3 11 July 2012 06:54AM

Today's post, Can Counterfactuals Be True? was originally published on 24 July 2008. A summary (taken from the LW wiki):

How can we explain counterfactuals having a truth value, if we don't talk about "nearby possible worlds" or any of the other explanations offered by philosophers?

Discuss the post here (rather than in the comments to the original post).

This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was When (Not) To Use Probabilities, and you can use the sequence_reruns tag or rss feed to follow the rest of the series.

Sequence reruns are a community-driven effort. You can participate by re-reading the sequence post, discussing it here, posting the next day's sequence reruns post, or summarizing forthcoming articles on the wiki. Go here for more details, or to have meta discussions about the Rerunning the Sequences series.

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Comment author: 12 July 2012 06:00:51AM 0 points [-]

Strictly speaking, counterfactuals must be true. If false then X is the same logical statement as If not X then True- which is true regardless of X.

When we go into hypotheticals is where things get interesting: cases where we make a statement in the same form as a counterfactual statement without knowing the truth value: If the mail has not been delivered today, my mailbox is empty. (This statement may be true or false; for this discussion we will consider the chances of it being false to be small.) By observation, there is mail in my mailbox. Therefore, the mail has been delivered today.

There is mail in my mailbox, therefore if the mail had not been delivered today, the sun would be exploding- this statement is now true with the same small chance of error that we ascribed to the original hypothetical statement.

For a less strict and more reasonable discussion of counterfactuals, speak about them as a future prediction made before the event- "If the mail is not delivered today, the sun will explode" appears false, even if the mail will be delivered today. In a deterministic universe where the mail will be delivered today, it is true only on a technicality.

Comment author: 12 July 2012 08:12:11AM 3 points [-]

Strictly speaking, counterfactuals must be true. If false then X is the same logical statement as If not X then True- which is true regardless of X.

You're treating counterfactuals as material conditionals. But there are many good reasons to think that counterfactuals are not simply material conditionals. One of the first observations that motivates work on the semantics of counterfactuals is exactly that some counterfactual sentences appear to be false -- despite having known-false antecedents.

Comment author: 16 July 2012 05:51:33PM -1 points [-]

In other words, people are bad at evaluating statements with known-false antecedents.