Argument Evaluation Part One Assessing the Inference Deductive

Argument Evaluation Part One: Assessing the Inference, Deductive and Inductive Reasoning

How do we know an argument is “good? ” What a “good” argument doesn’t mean: A. “Good Argument” does not mean “Agrees With My Views. ” B. “Good Argument” does not mean “Persuasive Argument. ” C. “Good Argument” does not mean “Well-Written or Well-Spoken Argument. ”

How do we know an argument is “good? ” � Two fundamental questions of argument evaluation 1. Do the premises, if true, provide adequate reason to believe the conclusion is true? 2. Are the premises true (plausible or acceptable)?

How do we know an argument is “good? ” What a “good” argument does mean A. Deductive arguments are good when they are sound. B. Inductive arguments are good when they are cogent.

What is a “sound” argument �Deductive �Valid inference �True premises

What is a “cogent” argument? �Inductive �Strong �True inference premises

Assessing the Inference � The inference in an argument is the process relationship of support between the premises and the conclusion. by which one asserts a conclusion on the basis of given evidence or reasons (i. e. drawing a conclusion from the premises).

How do I know when an argument is Deductive or Inductive? � How certain does the author intend their inference to be? ◦ If the author intends for their inference to be certain or necessary, the argument should be treated as a deductive argument. ◦ If the author intends for their inference to be probable or likely, the argument should be treated as an inductive argument.

How do I know when an argument is Deductive or Inductive? � Tests for determining author’s intent: 1. Indicator Word Test 2. Strict Necessity Test 3. Common Pattern Test 4. Principle of Charity 5. Exceptions to Strict Necessity

How do I know when an argument is Deductive or Inductive? � Indicator Word Test ◦ Does the author employ indicators in their conclusion that convey the intent of establishing a certain or necessary inference? ◦ Phrases like, “necessarily, ” “it must be the case that, ” “it is certain that, ” “obviously, ” “it logically follows that, ” etc. indicate that the author intends to establish a deductive argument. ◦ Phrases like, “probably, ” “it is likely that, ” “it is reasonable to conclude, ” etc. indicate that the author intends to establish an inductive argument.

How do I know when an argument is Deductive or Inductive? � Strict Necessity: Does the conclusion follow with strict logical necessity from the premises? ◦ Scenario Method: Is it possible to imagine some scenario (however strange) where the premises could be true and at the same time the conclusion would be false? ◦ If yes, then the argument does not meet the standard of strict necessity.

How do I know when an argument is Deductive or Inductive? � Common Pattern Test: Does the author employ a common pattern of reasoning that is characteristically deductive/inductive?

How do I know when an argument is Deductive or Inductive? � Principle of Charity: We should give the author the benefit of any doubt. When it is reasonable to treat an argument as having a fairly good inductive inference, but where treating the argument as deductive would lead to rejecting the argument, we should treat the argument as inductive.

How do I know when an argument is Deductive or Inductive? � Exceptions to Strict Necessity: An argument in which the conclusion does not follow necessarily from the premises should nonetheless be treated as deductive if either 1. The language or context makes clear that the author intended to offer a logically conclusive inference; 2. The argument has a pattern of reasoning that is characteristically deductive, and nothing else about the argument clearly indicates it is meant to be inductive.

Assessing the Inference � What is a “good” inference? 1. In a deductive argument, a good inference is a valid inference. 2. In an inductive argument, a good inference is a strong inference.

Deduction: What is a Valid Inference? � A valid deductive argument is one that establishes its conclusion with Strict Logical Necessity or Absolute Inferential Security. Which is to say, in a Valid argument: ◦ If the premises are (taken to be) true, then the conclusion must also be (taken to be) true. ◦ The conclusion follows necessarily from the premises. ◦ The premises provide logically conclusive grounds for the truth of the conclusion. ◦ The premises guarantee the conclusion. ◦ It is logically inconsistent to assert all the premises are true and at the same time deny the conclusion. ◦ It is impossible for the premises to be true and the conclusion to be false.

Deduction: What is a Valid Inference? � Some things to watch out for ◦ “Valid” does not mean “true” ◦ An argument can have a valid inference, even if the premises are false. ◦ An argument can have a valid inference, even if the conclusion is false. All whales are fish. All fish have gills. All whales have gills.

Deduction: What is a Valid Inference? � Some more tips regarding Validity: 1. Validity admits of no degrees, an argument is either valid or invalid. 2. An inference cannot be “pretty valid” or “nearly valid, ” but is either 100% valid or 100% invalid

Induction: What is a Strong Inference? �A strong inductive argument is one that establishes its conclusion with probability. Which is to say, in a Strong argument: ◦ If the premises are taken to be true, then the conclusion is likely ◦ The premises provide good reasons, though not logically conclusive ones, to accept the conclusion. ◦ The premises make the conclusion of the argument more likely than any other possible conclusions drawn from the same evidence.

Induction: What is a Strong Inference? ◦ “Strong” does not mean “true” ◦ An argument can have a strong inference, even if the premises are false. ◦ An argument can have a strong inference, even if the conclusion is false. In a study of 10, 000 dental patients, people who brushed their teeth regularly (at least two times a day) for years did not have a lower rate of tooth decay than those who do not brush regularly. Thus, brushing your teeth does not help prevent tooth decay.

Induction: What is a Strong Inference? � Some more tips regarding inductive strength: ◦ Inductive strength admits of degrees, an argument can be moderately strong or very strong. ◦ Even the best inductive inference still leaves some room for doubt regarding the conclusion. ◦ Often, the inference in an argument can be made more strong if the conclusion is appropriately qualified to match the degree of evidence.