Chapter III Evaluating Arguments

Nondeductive Arguments Most common kinds of arguments Successful arguments are a matter of degree. Deal with likelihood and probability – These kinds of arguments commonly build cases to establish strength. Are never failsafe. Plausibility determines strength

Deductive Arguments One statement deductively entails another if and only if it is impossible for the second one to be false, given that the first one is true. That is, the state of affairs in which statement (1) is true and statement (2) is false is logically impossible. That a person is a sister deductively entails that she is female, becuase it is a logical impossibility (inconceivable) for a person to be a sister and not be female.

Argument Possibilities FalseFalseTrueTrue FalseTrueTrueFalse Invalid ValidValidValidInvalid

Deductive Arguments Failsafe – Conclusion is guaranteed by the premise(s). Example: – If the battery is charged, the car will start. – The battery is charged. – The car will start.

Deductive Arguments Valid (necessary, absolute) – “Validity is a matter of support that a set of premises lends to a conclusion. It is a question of whether a certain relationship holds between premises and conclusion. (If we grant the premises must we grant the conclusion?) Hence validity does not require the premises of an argument to be true. Daniel Alfredsson is a turtle, all turtles are great hockey players. Therefore, Daniel Alfredsson is a great hockey player.

Sound Arguments Gold standard of arguments – Premise(s) are true + form is deductive. – Valid and true. – Example: North America is in the Western Hemisphere. Canada part of North America. Canada is in the Western Hemisphere.

Truth is Not Realtive

Truth And those whose hearts are fixed on Reality itself deserve the title of Philosophers. - Plato, Republic The logic of the world is prior to all truth and falsehood. – Ludwig Wittgenstein Aristotle – Law of Identity an object is the same as itself: A ≡ A. Or the Law of Noncontradiction (A cannot = not A). In other words, I cannot both be my self and not myself at the same time.

Against Relativism Points of view having no absolute truth, and have only relative, subjective values according to differences in perception and consideration. No necessary universal right or wrong, judgments are subject to the context (situation). Postmodernism – Modern era was a quest for progress, enlightenment. – Incredulity to metanarratives – Jean Francois Lyotard

Reason/Logic Trust in the proposition that there is a general Good (Plato) Universal, necessary, atemporal, asituational, objective... Cf. Mathematics University – Vs. Subjective, particualr, temporal, context, relative, “multiversity”.

Nondeductive Arguments are Not Relative Page 43. – 1) “are not meant to be valid, but they are meant to make their conclusions probable or likely” – 2) “addition of new information in the premises of a nondeductive argument may radically alter the overall amount of support we have for the conclusion” – 3) “successful if it is nondeductive and its premises make its conclusion more likely than not” “more likely than not”? – principle of democracy? Majority rule – What about “beyond a reasonable doubt”?

Complex Arguments Page 50 “The general point here is that in any nonvalid inference, even those that are nondeductively successful, some loss of certainty occurs, and the loss of certainty accumulates with each additional step in a series of inferences. The result may be an argument that is, overall, unsuccessful.” Character of the argument always defaults to the invalid inference. Example: – Multiple valid inferences & 1 invalid inference = Invalid arugument