Many people associate logic with brain teasers and mathematical puzzles, which seem to have little relevance to real life. The truth is that logic is of great practical significance. If your friend is in New Zealand, you know she is not in Japan. This piece of everyday reasoning involves logic. The core of logic is about consistency and deduction, both of which are indispensable for everyday thinking, not to mention scientific research and legal reasoning. Logic also plays a special role in computer technology. Computers are good at processing information because their processors can perform a huge number of logical operations very quickly. Obviously, normal people are capable of logical reasoning to some extent, or else we would not be able to survive very long! But making the effort to study some logic can improve our understanding of what good reasoning is like so we can become even better. In this chapter we shall look at some basic concepts of logic.

7.1.1 Consistency

A set of statements is consistent when and only when it is logically possible for all of them to, be true in the same situation. Otherwise they are inconsistent. So for example, “Adrian is happy” and “Adrian is married” are consistent with each other since there is no reason why a married person cannot be happy. On the other hand, “Visanna is 30 years old” and “Visanna is 20 years old” are obviously inconsistent. Here are a few more points to remember about consistency: ...

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