Critical thinking chapter 3 PDF

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Making Sense of Arguments To recognize an argument, you must be able to identify the premises and the conclusion. Indicator words such as because and since often signal the presence of premises, and words such as therefore and thus can point to a conclusion

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Argument Basics The point of devising an argument is to try to show that a statement, or claim, is worthy of acceptance. The point of evaluating an argument is to see whether this task has been successful-whether the argument shows that the statement (the conclusion) is worthy of acceptance Different ways that an argument can be good or bad because there are different types of arguments Arguments come in deductive and inductive Deductive argument is intended to provide logically conclusive support Inductive argument is intended to provide probable -not conclusive- support for its conclusion A deductive argument that succeeds in providing such decisive logical support is said to be valid; a deductive argument that fails to provide such support is said to be invalid. A deductively valid argument is such that if its premises are true, its conclusion must be true Because of the guarantee of truth in the conclusion, deductively valid arguments are said to be truth-preserving. EX. a. All men are mortal Socrates is a man Therefore, Socrates is mortal NOT EX. b. All dogs are mammals All cows are mammals Therefore, all dogs are cows An inductive argument that succeeds in providing probable but not conclusivelogical support for its conclusion is said to be strong An inductive argument that fails to provide such support is said to be weak the structure of an inductively strong argument cannot guarantee that the conclusion is true if the premises are true. Because the truth of the conclusion truth-preserving

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Ninety-eight percent of Humans are mortal. Socrates is human. Therefore, Socrates is likely to be mortal Logical validity or logical strength is an essential characteristic of good arguments. Good arguments also have true premises. A good argument is one that has proper structure and true premises c.

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EX. d. All pigs can fly. Vaughn is a pig Therefore, Vaughn can fly  

A deductively valid argument that has true premises is said to be sound. A sound argument gives you good reason for accepting its conclusion When inductively strong arguments have true premises, they are said to be cogent. Good inductive arguments are cogent

Judging Arguments Steps to determine whether is inductive or deductive Step 1. Find the arguments conclusion and premises Step 2. Ask: Is it the case that if the premises are true the conclusion must be true? If the answer is yes, treat the argument as deductive Step 3. Ask: Is it the case that if the premises are true, its conclusion is probably true? If the answer is yes, treat the argument as inductive Step 4. Ask: Is the argument intended to offer conclusive or probable support for its conclusion but fails to do so? If you reach this step, you will have already eliminated two possibilities: a valid argument and a strong one  

Terms that signal a deductive argument include “ It necessarily follows that,” “it logically follows that,” “absolutely,” “necessarily,” and “certainly” Words signaling an inductive argument include “likely”, “probably,” “chances are,” “odds are,” and “it is plausible that.”

Finding Missing Parts 

Arguments can have a piece missing (premises or conclusions are left unstated)

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EX. a) The easy availability of assault rifles in the United States has increased the risk of death and injury for society as a whole. Therefore, assault rifles should be banned. In the example there is a premise missing. Premise and conclusion are disconnected “Anything that increases the risk of death and injury for society as a whole should be banned” would be good additional premises Be aware though that many times the problem with an argument is not unstated premises, but invalid or weak structure

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EX. a) If Tariq works harder, he will pass his calculus course. But he will not work harder, so he will not pass his calculus.

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To make sure that your investigation of implicit premises is thorough and reasonable, work through the following three-step process Step 1: search for a credible premise that would make the argument valid. Choose one that is most plausible and best fits best with the author’s intent Step 2: Search for a credible premise that would make the argument as strong as possible Step 3: Evaluate the reconstituted argument

Argument Patterns 

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If p, then q. p. Therefore, q. First line in the argument is a compound statement- it’s composed of at least two constituent statements Conditional (premise) the if part is known as the antecedent the then part is known as the consequent pattern shown here is called affirming the antecedent or modus ponens Any argument in the modus ponens form is valid -if the premises are true, the conclusion absolutely must be true. If it’s in the form of modus ponens, it’s valid, regardless of the content of the statements Another common argument form is called denying the consequent, or modus tollens If p, then q. Not p. Therefore, not p. Modus tollens is always valid Hypothetical syllogism “hypothetical” is just another term for conditional. A syllogism is a deductive argument made up of three statements-two premises and a conclusion In a hypothetical syllogism, all three statements are conditional, and the argument is always valid If p, then q. If q, then r. Therefore, if p, then r. There are two common argument forms that are not valid. One is called denying the antecedent If p, then q. Not p. Therefore, not q. The other common invalid form is affirming the consequent If p, then q. q. Therefore, p. Disjunctive syllogism is valid and extremely simple

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Either p or q. Not p. Therefore, q. Either disjunctive can be denied not just the first one...