Evaluating Deductive Reasoning Determine whether the argument’s form (or structure) is valid or invalid. Decide if the premises are true or false. A sound argument has both a valid form and true premises. An unsound argument has either an invalid form, a false premise, or both.

Deduction and Induction In inductive reasoning, the premises provide probabilistic support for the conclusion. Pace courses meet on Saturdays. Since Michelle drove off Saturday with her book bag, she is probably taking a PACE course. In deductive reasoning, the premises provide conclusive support for the truth of the conclusion. Any student who has completed 12 or more units with a GPA of 3.0 or higher is eligible to join Alpha Gamma Sigma. Gina has completed 24 units and her GPA is 3.2. Therefore, Gina is eligible to join Alpha Gamma Sigma.

Signal Words Words like must, certainly, and necessarily frequently signal deductive reasoning. No Muslims eat pork. Since Tariq loves ham, he must not be a Muslim. Words or phrases like probably, likely, it is reasonable to conclude, it is plausible that, usually signal inductive reasoning. Rose reads her Bible at work, so she is probably a believer.

Inductive or Deductive? A profession of certainty in matters of religion is always a sign of religious illiteracy. Since McArthur professes to be certain about the truth of his religious beliefs, we can infer that he is illiterate about religion. People who think we are living in the “last days” of the universe are usually not environmentalists. Since Hal believes we are living in the “last days,” it is safe to conclude that he is not an environmentalist. The Pope insists that Catholicism is the only religion that is fully correct. Thus, the Pope is not a pluralist.

Deductive Validity \ Helen is pious. P N H A deductive argument is valid when it is impossible for the conclusion to be false, if we presume that the premises are true. All nuns are pious. Helen is a nun. \ Helen is pious. P N H

Deductive Arguments Information content of the conclusion is contained in the premises. All artists are bohemians. All bohemians are creative. \ All artists are creative. All A are B All B are C \ All A are C

Different content, same form All panthers are predators. All predators are carnivores. \ All panthers are carnivores. All A’s are B’s All B’s are C’s \ All A’s are C’s

Sound=Valid form + true prem.s All LAMC students are stressed people. All stressed people are addicted to either, alcohol, tobacco, chocolate, caffeine, exercise, or religion. \ All LAMC students are addicted to either alcohol, tobacco, chocolate, caffeine, exercise, or religion. Unsound?

What’s the missing Premise? What am I wearing, All psychics are pseudoscientists. That’s why all psychics are unreliable. psychic friend?

What Conclusion Follows? What’s in that sandwich? All Adventists are vegetarians. All vegetarians are guiltless eaters. \ ? Logicians Do it Deductively

Formal Fallacies All Mormons are supernaturalists. All Christians are supernaturalists. \ All Mormons are Christians. Valid or invalid? All A’s are B’s All C’s are B’s \ A’s are C’s

Refutation by formal analogy All nuns are people All priests are people \ All nuns are priests Same form, but obviously true premises and false conclusion shows that the form is invalid. All A is B All C is B All A is C

Categorical Logic A syllogism is an argument having two premises and a conclusion. A categorical syllogism is made up of assertions about class membership. There are four types of categorical assertions. A: Universal affirmative: All Muslims are monotheists. E: Universal Negative: No Nuns are Priests.

Particular Categorical Assertions I: Particular affirmative: Some novelists are alcoholics. O: Particular negative: Some Hindus are not vegetarians. Overlapping circles can represent these assertions. Some kittens are playful.