Saturday, October 20, 2007

4 Types of Logical Evidence

If all men are mortal, and Socrates is a man, it is evidence that Socrates is mortal.  This type of evidence is conclusive.  It is as airtight as accurate mathematical statements like 2 + 2 = 4.  If the premises are true, and the reasoning is "valid", then the argument is "sound". This is called deduction.

If all pictures observed hang on nails, it is evidence that all pictures hang on nails. This type of evidence is not conclusive like deduction is. It is called strong induction.

If I always hang pictures on nails, it is evidence that all pictures hang on nails. This type of evidence is weaker than strong induction, so it is called weak induction.

There is one other type of logical evidence, called abduction.  Abductive reasoning involves using your imagination to speculate about the likely cause of a phenomenon - inferring the best explanation.  The jury is still out regarding how abduction should be performed and how strong abductive evidence is.

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