1.7 Basic Logic

Back to 1.6 Evidence Defined

1.7.1 Of course, evidence doesn't speak for itself. We must be able to process the information that evidence provides. A bloody glove, a batch of statistics, a fossil - what do these mean? Logic is an important part of being able to handle evidence properly because, if our logic is faulty, then the best evidence in the world will still lead us to false conclusions.

1.7.2 Without going into a complete course on logic, I will attempt to highlight some important areas. The basic structure of a logical argument is a list of premises, which support a conclusion. At least two requirements have to pass muster if the argument is to be considered logical: 1) each and every single premise in the argument must be true (these premises can be basic proven facts, raw pieces of evidence, or conclusions from previous arguments, which have been shown to be valid and true) and 2) the conclusion must follow from the premises. If either of these two requirements is not met, then the argument is suspect.

1.7.3 Let's look at an argument where the first requirement is not met:

premise #1: All dogs have psychic powers.
premise #2: Lassie was a dog.
conclusion: Lassie had psychic powers.

The interesting point about this argument is that it is both logically valid and false. The conclusion does follow from the premises so the structure of the argument is logical. However, while premise #2 is true, premise #1 is not and therefore the entire argument is tainted, leading to a false conclusion.

1.7.4 Now let's look at an argument where the second requirement is not met:

premise #1: Superman wears a red cape.
premise #2: Batman is a comic hero.
conclusion: Batman wears a red cape.

In this case, we have an argument where every single premise is true. However, the conclusion does not follow from the premises listed and it is therefore false.

1.7.5 There are many other aspects to casual logic, including several other logical fallacies such as: circular reasoning, over generalization, statistical misuses, false analogies, etc. The reader should look into other works on logic for further detail.

Continue to 1.8 The Contextual Judgment Principle