A cat is a table

Cats have four legs. Tables have four legs. A cat is therefore a table.

Words by themselves do not always tell the whole truth. There is nothing wrong with the vocabulary, spelling or structure of those sentences. The logic has gone astray. The previous section "Lines of thought" referred to personal logic. Here is a rather unusual example of personal logic. It is from a book of anecdotes published in 1864.

In 1685, the widow of the Duke of Monmouth sent a pound of tea (about half a kilogram) to one of her relations in Scotland. This Chinese product was then unknown in western countries. The family examined it closely, and ordered the cook to come. After studying it for a long time, he decided that it was a dried herb or vegetable. He boiled the leaves, threw the water away, and served up the leaves as if they were spinach. The ladies and gentlemen did not enjoy this new vegetable at all.

The cook applied his logic: The leaves look like a dried vegetable of some sort. We boil vegetables and serve them on a plate. He was not aware of the existence of tea-leaves. His logic was based on his experience. You could possibly devise other tales about people being confronted with something they have never seen before. Imagine, for instance, extra-terrestrials arriving on Earth. The first living creatures they see are cows, lots of cows. They see only a couple of humans in the distance, or half-hidden in motor vehicles. What are their conclusions? How do they distort what we know to be the truth?

In the matter of the cat and the table, we are dealing with what we know. The facts are: a cat is an animal with fur; a table is an item of furniture. True, it is possible that people in some countries might not have seen a cat. In other places, people might not have seen a four-legged table. But we are looking at what is general knowledge for us. Try this one:

1. Cats are animals, have four legs, fur, a tail and whiskers, and are kept as pets.
2. Dogs are animals, have four legs, fur, a tail and whiskers, and are kept as pets.
3. Therefore a dog is a cat.

There is plenty of information in those statements, but what is missing?

Because we use language to communicate ideas, we have to take care that we use it clearly. There is a danger in using too few words as well as too many. There is also a risk that we might generalise. This happens when we take just a few facts about, say, a person and apply them to all similar people. It is not logical to say that because one, or a few, people of a particular type do a certain thing, then all people of that type do the same thing. It doesn’t matter how well you express your “facts” — if they are not complete, you observation is
not logical. It might be your personal opinion but it is not factual if it is based on limited or selected evidence.

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