Logic

i.e. the study of argument and the use of reason

-- in other words, logic is the study of thinking

Logic:

• does not deal with all mental phenomena (learning, remembering, daydreaming, etc.), but only with that type of thinking called “reasoning.”

• differs from Psychology

Logic

• is not concerned with emotional states at all, or with the “inner processes” going on in the mind of the thinker.

Logic

• is concerned only with reasoning itself, and the formulation of rules that will help us determine if any particular piece of reasoning is logical; i.e. coherent and consistent.

The Structure of Argument

• The basic unit of logic is the proposition or statement, typically expressed in a declarative sentence:

e.g. “Smith loves Jones.”

“Socrates is mortal.”

The Structure of Argument

• The key characteristic of each proposition is that it can be either true or false, but not both.

e.g. Either “Socrates is a man”is true, or “Socrates is not aman” is true -- but not both.

The Structure of Argument

• The chief concern of logic is how the truth of some propositions (premises) is connected with the truth of another (the conclusion).

The Structure of Argument

For example:

All men are mortal. (premise)

Socrates is a man. (premise)

Socrates is mortal. (conclusion)

The Structure of Argument

• The pattern of logic that lets us connect these premises to arrive at the conclusion we call an inference.

The Structure of Argument

• Without this pattern of inference, we have merely a collection of disjointed propositions.

e.g.“My dog has fleas.”

“The moon is made of cheese.”“Strawberries are red.”

The Structure of Argument

• Our primary concern is to evaluate the reliability of inferences, the patterns of reasoning that lead from premises to conclusion in a valid argument.