CriticalThinking Tutorial 12

1 Chapter 9: Deductive ReasoningWhat distinguishes deductive reasoning from inductive reasoning is that in inductive arguments,if they are sound, the conclusion is merely supported by the premises, whereas in deductivereasoning, if the argument is sound, then the conclusion is guaranteed. Recall that the definitionof soundness is that an argument is sound iff it has a high degree of logical strength and thepremises are true, and recall the definition of logical strength is that if the premises are true,then they provide some degree of support for the conclusion. In the case of deductive argumentsthe degree of logical strength is the highest possible, the truth of the premises guarantees thetruth of the conclusion. Arguments with this property are called valid arguments.valid argument: An argument is valid iff the truth of the premises guarantees the truth of theconclusion.Thus, valid arguments enable us to derive true statements from true statements.An example of a deductive argument is the following:She will order coffee or scotch with her lunch. She won’t order scotch, so she willorder coffee.The truth of the first two premises guarantees the truth of the conclusion. You may notice,however, that there is nothing about the particular premises that makes the argument valid.Any argument of the same formp or qnot-p∴ qwill also be valid. This illustrates that validity is a property of the form of the argument, and notits content, i.e., validity is independent ...