A lot of everyday thinking, and not a little academic thinking, is riddled with logical fallacies. It pays to know what counts as logical thinking, in order to keep one’s mind on the straight and narrow.
Here are some notes, helpfully summarised from Peter Kreeft’s book Socratic Logic by Justin Taylor:-
There are three kinds of thoughts, or three acts of the mind:
- Simple apprehension [understanding a simple term—e.g., “man”]
- Judging [relating two concepts by predicating one term of the other—e.g., “man is mortal”]
- Reasoning [relating two or more judgments with a conclusion—e.g., “man is mortal; I’m a man; therefore I’m mortal”]
These three acts of the mind result in three mental products:
- Concepts (the products of conceiving)
- Judgments (the products of judging)
- Arguments (the products of reasoning, or arguing)
Expressed logically these are:
- Arguments (most commonly, syllogisms)
These logical entities answer the three most fundamental questions:
- A term answers what something is.
- A proposition answers whether something is.
- An argument answers why it is.
These logical entities also reveal three aspects of reality:
- Terms reveal essences (what something is).
- Propositions reveal existence (whether something is).
- Arguments reveal causes (why something is).
These logical entities can be judged logically good or logically bad:
- Terms are either clear or unclear (=ambiguous).
- Propositions are either true or false.
- Arguments are either valid or invalid.
To make a convincing argument you have to fulfill all three of the following conditions:
- Your terms are clear.
- Your premises are true.
- Your logic is valid.
If you want to critique someone’s argument, you have to show an error in just one of the following:
- They are using a term ambiguously.
- They are using a false premise.
- They are committing a logical fallacy (i.e., the argument is invalid; the conclusion does not follow from the premises).