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Suppose it has been fully established that event x causes event y, in circumstance a. Would it be possible to correctly deduce that event x is occuring purely by observing that event y is occuring in circumstance a? Or can the same effect (in the same conditions) have multiple causes?

asked Feb 03 '11 at 15:05

JWilliams's gravatar image


edited Feb 03 '11 at 15:52

Greg%20Perkins's gravatar image

Greg Perkins ♦♦

There is a logical fallacy which captures the trouble here, called Affirming the Consequent.

Informally, it is the pattern of arguing anything like: "(1) If it is raining, then the ground will be wet. (2) The ground is wet. (3) Therefore, it is raining." This is invalid because there might be other causes of the ground being wet -- like someone spraying water on it from a hose.

More formally, it is the pattern of arguing:

  • Premise 1: If A then B
  • Premise 2: B
  • (Invalid) Conclusion: Therefore A

You hinted at the way through this, though: what must be established in your example isn't just that x causes y, but that only x causes y. Here is a valid logical pattern that would reflect that idea:

  • Premise 1: If-and-only-if A then B
  • Premise 2: B
  • (Valid) Conclusion: A

Whether you can establish that y has exactly one cause depends on y: some things do, some things don't.

answered Feb 03 '11 at 16:14

Greg%20Perkins's gravatar image

Greg Perkins ♦♦

Thanks for your answer--makes perfect sense.

(Feb 04 '11 at 11:07) JWilliams JWilliams's gravatar image

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Asked: Feb 03 '11 at 15:05

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Last updated: Feb 04 '11 at 11:07