Logic 1.1

Logic is the organized body of knowledge or science that evaluates arguments.

Aim: to develop a system of methods and principles that we may use as criteria for evaluating the arguments of others and as guides for constructing our own.

Effect: Gain confidence in making and criticizing arguments.

Arguments: Claims that support a conclusion.

Two Types: Those that do support a conclusion, and those that do not do so.

Exs:

Statements: A sentence that is either true or false

What are some T/F statements?

Why are they T/F?

Truth-Value: The truth or falsity of a statement.

Questions, Proposals, Commands, Suggestions, Exclamations have no truth-value. Why not?

The statements that make up an argument fall into two classes:

The conclusion is supposed to follow, be supported by (the evidence) premises. Consider the application to science: evidence stands as the premises of a scientific conclusion.

What kind of entailment (“following through”) is involved? Induction? Deduction? Which is stronger? Why? How has this distinction been important in the history of philosophy?

Exs of good and bad arguments:

Conclusion Indicators: therefore, hence, so, etc.

Premise Indicators: since, because, for, etc.

Not all statements will have clear indicators. You must carefully and critically read for sense.

E.g.,

Often the first or last statement in a paragraph is the conclusion, but not always.

Demonstration of an argument:

“Since {P1} the secondary light [from the moon] does not inherently belong to the moon and {P2} is not received from any star or {P3} from the sun, and {P4} since in the whole universe there is no other body left but the earth, what must we conclude? Surely we must assert that {C} the lunar body (or any other dark and sunless orb) is illuminated by the earth. G. Galilei, The Starry Messenger)

Try to retain as much of the original as possible.

Exclude whatever is unnecessary in the statement.

Inference: The reasoning process expressed by an argument (for our purposes, synonymous with argument).

Proposition: The meaning, or information content, of a statement (for our purposes, synonymous).