The Art of Logic

The key is to remember that it is both statements “A” and “A implies B” that together allow us to infer statement B. So if statement B is not true it is either because A isn’t true or because “A implies B” isn’t true. The possibility of the implication being untrue is often overlooked.

A is a sufficient condition for B. B is a necessary condition for A. • A is true only if B is true. Only if B is true is A true.

many arguments in real life go wrong because of problems with the groundwork rather than with the argument per se.

soundly but starting from different basic beliefs. So two people can both be logical but still disagree about things.

The primary aim of normal language is communication, whereas the primary aim of logical language is to eliminate ambiguity.

Time and causation flow in one direction only, and so does logic, and we must be careful not to make errors in direction.

In that situation the key would be to change someone’s mind about that core principle rather than anything else.

A powerful aspect of abstraction is that many different situations become the same when you forget some details.

be true, not by cause and effect, not by probability, not by observation, but by something inherent that will never ever change.