Friday Fallacy – Illicit Minor

If you have not yet read last week's fallacy on the fallacy of the undistributed middle read that first, as this week's post will only make sense in light of that post.

Like the fallacy of the undistributed middle, illicit minor is also a syllogistic fallacy, and the form is fairly similar. The fallacy of the undistributed middle had the form:

All A are B;
All C are B;
Therefore, all C are A.

Illicit minor has the form:

All A are B;
All A are C;
Therefore, all C are B.

For example:

All animal rights activists are vegans;
All animal rights activists are humans;
Therefore, all humans are vegans.

As pleasant as this conclusion is, we clearly have yet to make it true. In a syllogism, the categorical proposition with the term that comes second in the conclusion, in this case, “all animal rights activists are humans,” is called the major premise, and the categorical proposition with the term that comes first in the conclusion, in this case, “all animal rights activists are vegans,” is called the minor premise. This syllogism is a fallacy because the minor term allows some humans to still not be animal rights activists, yet our conclusion tries to draw from the animal rights activist property of humans in order to draw its conclusion. The name illicit minor derives from the fact that the minor premise does not describe all of the individuals who are described as the subject in the conclusion.

It is still possible for syllogisms of this form to have true conclusions. One example might be:

All cats are animals
All cats are mammals
Therefore, all mammals are animals.

This conclusion is technically true, but it cannot be derived from the two premises given. The fact that the conclusion does not necessarily follow from the premises is what makes an argument a fallacy, not that it is necessarily false.

You may have noticed that last week's fallacy was a bit sparse on the examples. That is because most good examples of syllogistic fallacies are actually cases of illicit minor. Remember that things like “I am an animal rights activist” is the syllogistic equivalent of “All 'me' are animal rights activists.” Here are a few examples of illicit minor in action:

The book The China Study cites studies where animals fed diets high in casein developed certain cancers at a much higher rate than those fed other diets. Casein is an animal protein. We cannot conclude from this, as the China Study attempts to do, that all diets high in animal protein will lead to higher rates of those cancers.

Roundup ready crops may contain unsafe levels of pesticide residue. Roundup ready crops are genetically modified. We cannot conclude from this that all genetically modified crops are necessarily unsafe even if Roundup ready ones are.

All of my blog's readers are becoming more skeptical. All of my blog's readers are or are becoming vegan. Sadly, this doesn't mean that all people who are or are becoming vegan are also becoming more skeptical.

Keep fighting the good fight for rights and reason everyone! More fallacies are on their way.