Logic and Critical Thinking Chapter 1 Study Guide

Invalid Deductive Argument

A deductive argument is invalid if and only if it is possible for the premises to be true and the conclusion false.

Sound Deductive Argument

A deductive argument is sound if and only if it is both valid and all its premises are actually true.

Unsound Deductive Argument

A deductive argument is unsound if and only if it is either invalid or has at least one actually false premise.

Valid Deductive Argument

A deductive argument is valid if and only if it is impossible for the premises to be true and the conclusion false, i.e., if the premises of the argument were true, then the conclusion would have to be true.

Premises

A proposition is a premise of an argument if and only if it functions in that argument as a proposition whose truth is supposed to give support to the truth of the argument's conclusion.

Conclusion

A proposition is the conclusion of an argument if and only if it functions in that argument as the proposition whose truth is supposed to be supported by the argument's premises.

Bad Argument

An argument is a bad argument if and only if it is an argument such that it either has at least one actually false premise or even were all its premises actually true, its conclusion is no more likely to be true than to be false.

Good Argument

An argument is a good argument if and only if it is either a sound deductive argument or a good inductive argument.

Deductive Argument

An argument is deductive if and only if it supposes that if the premises of the argument were true, then its conclusion would have to be true.

Inductive Argument

An argument is inductive if and only if its conclusion is supposed to be made more likely to be true than to be false given the truth of its premises, i.e., inductive arguments suppose that if their premises were true then their conclusion would be more likely to be true than to be false.

Bad Inductive Argument

An inductive argument is bad if and only if it is either weak or has at least one actually false premise.

Good Inductive Argument

An inductive argument is good if and only if it is both strong and all its premises are actually true.

Strong Inductive Argument

An inductive argument is strong if and only if the argument is such that if the premises of the argument were true, then the conclusion would be more likely to be true than to be false.

Weak Inductive Argument

An inductive argument is weak if and only if the argument is such that if the premises of the argument were true, then the conclusion would be less likely, or no more likely to be true than to be false.

Argument

Something is an argument if and only if it is a set of propositions such that the truth of one, the conclusion, is supposed to be supported by the truth of the others, the premises.

The difference between Deductive argument and Inductive argument

The primary difference between inductive arguments and deductive arguments is whether the support relation that is supposed to hold between the premises and the conclusion of the argument is one of likelihood or probability, in inductive arguments, making the claim that if the premises were true then the conclusion would be more likely to be true than to be false, or one of necessity, in deductive arguments, making the claim that if the premises were true then the conclusion would have to be true.