Jason Mathias

What fallacies are in this anti vaxxer meme?

Leukemia is the most common type of cancer in children. 

Formaldehyde is known to cause Leukemia, and other cancers. 

Formaldehyde is an ingredient in vaccines. 

Therefore, vaccines are causing Leukemia in children. 

Therefore, don't vaccinate your children. 


asked on Saturday, Sep 12, 2020 08:32:10 AM by Jason Mathias

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Bo Bennett, PhD

First there is a common scientific misunderstanding; the disentanglement of substance and quantity. Everything is poisonous or toxic given the right quantities. That which is deadly in high amounts can be life-saving in reasonable amounts. People are swayed more by the emotion of something being "toxic" that they can't grasp the quantity element of the equation.

It is important to note that we are dealing with an inductive line of reasoning, not a deductive argument where the conclusion is guaranteed by the truth of the premises (assuming the argument is valid).

Formaldehyde is known to cause Leukemia, and other cancers. 

Sure. But at what amounts? Nicotine is known to cause lung cancer, but a 13-year-old taking one puff of a cigarette will almost certainly not result in cancer.

Formaldehyde is an ingredient in vaccines.

This is ambiguous. Is it in all vaccines? Some?

Therefore, vaccines are causing Leukemia in children.  

We skipped the premise where we need to state that children are getting vaccines. Nit-picking, but worth noting on this forum. We have a basic non sequitur . As mentioned, we have several problems:

1) there is no mention of dosage or quantity that is known to cause cancer
2) assuming the dosage is cancerous, we need to be clear that the conclusion only applies to vaccines with that dosage of Formaldehyde
3) Vaccines cause Leukemia in how many children? How many children's lives are saved by vaccines? We can say that this is a form of cherry picking by focusing on the cons but and ignoring the pros.

The second conclusion is unwarranted without the statistical information needed (see point #3).

To demonstrate the problems, we can use an analogous argument:

Calories are known to cause obesity in children.
Calories are in food.
Therefore, food causes obesity.
Therefore, don't feed your children.


answered on Saturday, Sep 12, 2020 09:13:20 AM by Bo Bennett, PhD

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Prof M writes:

An excellent answer and discussion, Bo.

Prof M

posted on Saturday, Sep 12, 2020 08:19:33 PM
Dr. Richard

Post Hoc is the most immediate fallacy that springs to mind. The Post Hoc Propter Hoc fallacy consists of the misidentification of the cause for an observed effect. Simply put: If X occurred before Y, then X caused Y. A person commits this fallacy whenever the link between premises (X) and conclusion (Y)  depends on an incorrect causal connection. 

For a common example, a man is standing on the courthouse steps waving his arms and chanting. When asked what he is doing (X) he explains he is keeping elephants out of the building (Y). You point out there are no elephants on the continent and his response is, “See, it works.” 

To work against Post Hoc error, you must question the supposition X causes Y and be certain X is well established as the premise leading to the conclusion Y. In other words, check your premises. 

Another way is to substitute another product for the one in question. For example, If I changed this to an infant who ate pureed baby food was later diagnosed with leukemia, therefor children should not eat --- or at least not eat pureed food --- the error is clear. 

 By the way, if vaccinations interest you, I recommend any of the books by Paul A. Offit, M.D., especially   his tribute to Maurice Hilleman, the father of modern vaccines, entitled “Vaccinated.”

answered on Sunday, Sep 13, 2020 10:50:38 AM by Dr. Richard

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I think it is a faulty analogy or argumentum ad ignorantiam!

Leukemia is the most common type of cancer in children.   -> OK.

Formaldehyde is known to cause Leukemia, and other cancers.   -> OK

Formaldehyde is an ingredient in vaccines.  -> OK

Therefore, vaccines are causing Leukemia in children. -> NO, because the dosage of formaldehyde is important which it is ignored here. The quantity used in vaccines are below any toxic levels. Just because it is analytical detectable, doesn´t mean it is harmful.

answered on Tuesday, Sep 15, 2020 03:05:27 AM by Mr.T

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