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.