Thinking and Computation - Thinking as Computation - page 14

Uninterpreted sentences

A first clue that one might be able to understand thinking as computation is to look at
a sentence of English as a purely symbolic structure made up of a sequence of words.
Consider this, for example:

The snark was a boojum.

This is a line from the poem The Hunting of the Snark , by Lewis Carroll, that was
intended to be nonsense. (What is this snark? What is a boojum?) Observe that if one
assumes that the sentence is true , even without knowing what the words snark and
boojum mean, one can answer certain questions:

What kind of thing was the snark?
(It was a boojum.)
Is it true that the snark was either a beejum or a boojum?
(Yes, because it was a boojum.)

If no boojum is ever a beejum, was the snark a beejum?
(No, it could not have been.)

What is an example of something that was a boojum?
(The snark, of course.)

The point is that one can provide appropriate answers to these questions without
having to know what the two symbols mean. This is the first step toward linking thinking
and computation. Some simple rules of logic make it possible to extract answers
directly from the sentence itself (viewed as a symbolic structure) without having to
determine first what the symbols snark and boojum stand for.
Now consider the following three examples:
1. My keys are in my coat pocket or on the fridge.
Nothing is in my coat pocket.
So: My keys are on the fridge.

2. Henry is in the basement or in the garden.
Nobody is in the basement.
So: Henry is in the garden.

3. Jill is married to George or Jack.

Nobody is married to George.
So: Jill is married to Jack.