think for yourself
With lots of examples. Fun stuff, mostly. Spot good thinking. Catch wonky thinking—there is plenty in TV commercials.
This isn’t a textbook. There are no quizzes. There are no chapters, either. This is a wiki on critical thinking. The full title has over 100 articles, linked and cross-linked—choose your path and move at your pace. Learn how to separate reasoning from fallacies.
Composition
Composition is a confusion caused by mixing categories.
- We saw marching bands, clowns, horses, and floats, but the parade never passed by.
The parade is not in the same category as the marching bands, clowns, horses, and floats.
- Every cell in my body is 90 percent water, so my body is 90 percent water. The moon has an effect on bodies of water. Therefore, the moon has an effect on me.
In this case, my body (as mostly water) and bodies of water are in the same category, so there is no error in saying the moon affects both, at least to different degrees.
Composition is a fallacy that concludes that something has a property because its parts have that property, even though the attribute cannot be transferred from part to whole.
- Molecules are in constant random motion. The marble statue of the lion outside the library is composed of molecules. Therefore, the statue is in continuous random motion.
- Each page in this large phone book can easily be torn in half, so the phone book can easily be torn in half.
It is claimed that if the parts have a particular property, the whole must have that property.
- The parts of the model are plastic, so the assembled airplane is plastic. Every part of the model can fit in its package, but it does not follow that the completed airplane can fit in its package.
- Atoms of an apple have mass, so the apple has mass. Every atom of the apple is invisible, but it does not follow that the apple is invisible.
The error lies in transferring attributes that cannot be transferred.
- The sports car is made of lightweight parts, so the car itself has a low mass. [Each part is light, but there are so many that the vehicle is heavy.]
- A government represents its people; people can be phoned, so a government can be phoned. [I tried to call the government, but people kept answering.]
Expansive Property is an exception to the fallacy of Composition.
Division
Division is a fallacy that concludes that the parts have a property because the whole has that property.
- Russia is big, so Russians must be big.
- If you like cake, you will like to eat its ingredients, such as raw eggs, butter, and flour.
Division assumes that whatever is true of a whole must be true of each part. As with the fallacy of Composition, the error lies in transferring properties that cannot be properly transferred.
- You claim to be bankrupt but work for a wealthy company, so you must be wealthy.
- People are made of cells. Human beings are conscious, so cells must be conscious.
The error is transferring properties (sometimes with humorous results) that cannot be properly transferred.
- A pregnant Irish couple with two children is nervous because they know that every third child born is Chinese.
- White sheep eat more than black sheep because there are more of them. Therefore, this particular white sheep eats more than the black sheep.
Weak Analogy
Weak Analogy is a fallacy in which the conclusion depends on a similarity irrelevant to the claim.
An Analogy is a comparison: A is like B, so if A has a particular property, B likely has a similar property. In a weak analogy, the items compared are significantly different or have few relevant similarities.
- A laxative capsule looks like a jelly bean so that it will be just as tasty.
- When water is poured on the top of a pile of rocks, it trickles down to the rocks on the bottom. Similarly, when rich people make lots of money, this money will trickle down to the poor.
