Thinking and Computation - Thinking as Computation - page 16

Is thinking logic?
So in the end, is thinking just logic? For anyone who has studied logic, this is not a
very plausible notion.
Suppose somebody at a party says,
George is a bachelor.
Here are some of the sentences that this logically entails:
Somebody is a bachelor.
George is either a bachelor or a pig farmer.
Not everyone is not a bachelor.
It is not the case that both George and Henry are not bachelors.
Sure enough, these sentences will all be true if the given sentence is; that is what
logical entailment does. But they are so very, very boring!
If you found out at a party that George was a bachelor, it is almost guaranteed that
we would not spend time going through logical entailments like these. You might
think about George (whom you might already know) or about what it means to be
a bachelor . Thinking seems to be so much richer than just dry logical entailments
because thinking seems to depend on what the words in a sentence mean .
In fact, the view that thinking is logic may seem so far off the mark that instead of
asking what is wrong with it, one might be tempted to ask what is right with it.
1.3.3 Using what is known: The web of belief
To get a glimmer of what could be right with it, one has to go back to the idea
of thinking: bringing knowledge to bear on an activity. In reaching the conclusions
about George the bachelor, no other knowledge was used. The search for logical
entailments is not from that one sentence alone but rather from that sentence together
with everything else that is already known.
Figure 1.5 shows some of the relevant facts that may be known about George the
bachelor. In this collection of sentences, the terms George , bachelor , man , and so on,
appear in many places, linking the sentences together in the same way that the term
frimble did in the sentences of the earlier example.
It is sometimes helpful to visualize the sentences as forming a kind of network , with
nodes for each of the terms and links between them according to the sentences in
which they appear. The network might look something like the one in figure 1.6. We
may not know who George is, for example, but we can see that the node for George
is connected to the node for Mary by way of the node for son . We may not know what