Phil 1102: Critical Thinking September 01, 2004

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Validity / Soundness Valid argument: an argument in which it is impossible for the premises to be true and the conclusion false. Sound argument: A valid argument with true premises.

Inference Tickets By reasoning, we produce new beliefs from old beliefs. The method of reasoning used determines which new beliefs we are entitled to infer. For example: –I believe that all frogs are green. –I believe that Bob is a frog.

More: If it will rain, then I will take my umbrella. I will not take my umbrella.

And more… Either you’re lying or I’m a monkey’s uncle. I’m not a monkey’s uncle.

And even more… If you don’t take the exam, you will fail the course. You didn’t take the exam.

And on.. All cats are felines. All felines are mammals.

And on… John is a bachelor.

And on… I believe that every swan I have ever seen is white. I believe that every swan everyone I know has ever seen is white.

The Point: Logic & Critical Thinking are the study of inference tickets: what beliefs we are entitled to infer under what conditions. before we get into too much detail, let’s look at our beliefs themselves…

What do we believe? 1.Adding salt to water makes it boil faster. 2.When cooking pasta, one must add oil to boiling water before adding the pasta. 3.Groundhogs are nocturnal. 4.Chipmunks climb trees. 5.Groundhogs do not (climb trees). 6.Only humans murder. 7.No one can feel my pain but me. 8.A bachelor is an available adult male.

More beliefs Eskimos have hundred(s) of words for snow. Dogs cannot see any colors (only black & white)

Where do these beliefs come from? Method of Tenacity Method of Authority A priori method Bacon’s true induction

The method of tenacity “The social impulse is against it. The man who adopts it will find that other men think differently from him, and it will be apt to occur to him, in some saner moment, that their opinions are quite as good as his own, and this will shake his confidence in his belief.” Really?

The method of authority “For the mass of mankind, then, there is perhaps no better method than this. It is their highest impulse to be intellectual slaves, then slaves they ought to remain.”

A priori method History of metaphysics based on conceptual analysis is rife with error.

The Hypothesis “There are real things; those realities affect our sense according to regular laws, and though our sensations are as different as our relations to objects yet, by taking advantage of the laws of perception, we can ascertain by reasoning how things really are, and any man, if he have sufficient experience and reason enough about it, will be led to the one true conclusion.”

True induction The source of knowledge must be something public. Science is, then, committed to the existence of a mind-independent reality. Science is committed to the notion of a law of reality. Science’s central purpose is to discover the mind-independent reality, which is the ‘true’ conclusion.

Is it circular? (The Gambler’s realism) The method can be used even if we are skeptical about the hypothesis (Not-even-Berkeley realism) No one can really doubt the existence of reality. (Bandwagon realism) Everybody’s doin’ it. [perhaps a better characterization would be ‘this is the natural way our minds work’] (Common realism) Previous success.