Proving the 'All Blonde Girls Have Blue Eyes' Fallacy Theorem

  • Thread starter courtrigrad
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In summary: You have already proven that G_1, G_2, and G_3 have blue eyes. You do not need to repeat the process for G_1 and G_2. This does not prove that all four girls have blue eyes. In summary, the theorem states that if there is at least one blonde girl with blue eyes in a collection of n blonde girls, then all n of them must have blue eyes. This is proven by showing that the statement is true for n=1, and then using induction to show that the statement is true for all values of n. The corollary states that all blonde girls must have blue eyes, as there is at least one blonde girl with blue eyes in existence.
  • #1
courtrigrad
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Theorem Given any collection of $ n$ blonde girls. If at least one of the girls has blue eyes, then all $ n$ of them have blue eyes.

Proof. The statement is obviously true for n = 1. The step from k to k+1 can be illustrated by going from n = 3 to n = 4. Assume, therefore, that the statement is true for n = 3 and let G_1,G_2,G_3,G_4 be four blonde girls, at least one of which, say G_1, has blue eyes. Taking G_1,G_2, and G_3 together and using the fact that the statement is true when n = 3, we find that G_2 and G_3 also have blue eyes. Repeating the process with G_1,G_2 and G_4, we find that G_4 has blue eyes. Thus all four have blue eyes. A similar argument allows us to make the step from k to k+1 in general.


Corollary. All blonde girls have blue eyes.

Proof. Since there exists at least one blonde girl with blue eyes, we can apply the foregoing result to the collection consisting of all blonde girls.

Does it have to do with how we arrived at [tex] k+1 [/tex]?

Thanks
 
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  • #2
Won't work for n=2: Let G_1 and G_2 be blonde girls and le't assume the theorem is true for n=1. If, for example G_1 is blonde, we can't take G_2 to the collection with her (that would be n=2), so we can't prove that G_2 is also blonde.

Hence the induction stops at n=1 and you'll never reach the step 3->4.

If you were guaranteed that the theorem is true for all pairs of blonde girls and I told you that my sister is blonde and has blue eyes then, yes, all blonde girls would have blue eyes.
 
  • #3
Repeating the process with G_1,G_2 and G_4, we find that G_4 has blue eyes.

That is a non sequitur.
 

1. What is the "All Blonde Girls Have Blue Eyes" Fallacy Theorem?

The "All Blonde Girls Have Blue Eyes" Fallacy Theorem is a statement that suggests all blonde girls have blue eyes, which is a false and unsupported claim. It is considered a fallacy because it is based on subjective observations and not factual evidence.

2. Why is this theorem considered a fallacy?

This theorem is considered a fallacy because it is not supported by scientific evidence. It relies on a biased and limited observation of a group of people and ignores the diversity within that group. It also fails to consider other factors that may influence physical characteristics such as hair and eye color.

3. What evidence disproves this theorem?

There is no scientific evidence that supports the claim that all blonde girls have blue eyes. In fact, there are countless examples of blonde girls with different eye colors, and studies have shown that hair and eye color are not genetically linked. This disproves the notion that one characteristic can determine the other.

4. Why do people tend to believe this fallacy?

People tend to believe this fallacy because of societal stereotypes and media representations of blonde girls. In movies, TV shows, and advertisements, blonde girls are often portrayed as having blue eyes, reinforcing the false belief. This can also lead to confirmation bias, where people only notice and remember instances that fit their belief and ignore those that don't.

5. How can this fallacy be debunked and corrected?

This fallacy can be debunked by providing factual evidence and educating people on the diversity of physical characteristics within a group. It is essential to challenge and question stereotypes and biases and to recognize that physical appearance does not determine one's identity or worth. By promoting inclusivity and diversity, we can correct this fallacy and embrace the uniqueness of individuals.

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