John Protzko

Fallacy of Causal Exclusion

Posted on | October 8, 2015 | No Comments

Fallacy of Causal Exclusion

The Fallacy of Causal Exclusion occurs when someone assumes that the phrase “X Causes Y” has an effect on the relation of other variables to Y.
This fallacy can come up in two instances:

Assume A, B, C, and X all are causes of Y.
The first instance is the following:

X causes Y;
therefore, A does not cause Y.

The second instance is:

X cannot cause Y because A causes Y.

Example of the first instance:

Researcher: We have therefore shown that doubling the salary of new parents causes their children to do better in school when they grow up. Therefore, the argument that there is a causal effect of genes on academic ability is wrong.

The reason this is fallacious is it assumes that the X to Y causal relationship affects the validity of an A to Y causal relationship. This is only acceptable when X and A are necessarily contradictory (for example, the presence AND the absence of oxygen).

Example of the second instance:

Researcher: …based on the following evidence, we can now say that changes in Dopaamine cause changes in how many numbers people can hold in their head at one time.
Talk Attendant: That’s ridiculous, Dopamine can’t cause changes in that because the neurotransmitter GABA is the cause.

This reasoning is fallacious because it assumes there can only be one cause (an extension of causal oversimplification). In addition, it assumes that the causal relationship from X to Y (in this case, Dopamine to working memory) is wrong because of the existence of a separate relationship between A and Y (in this case, GABA to working memory).

Again, this may only be acceptable when X and A are necessarily contradictory. When X and A (or any other cause) are not contradictory, the argument is fallacious.

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