Natural Deduction Two
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Uploader Comments (kyphilosopher)
Top Comments
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still lost
2 years ago 3
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Evey time the screen refreshes with a new step my vision blurs lol, at least thats only temporary unlike my headache
All Comments (9)
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This is an odd feature of natural proofs at this level.
Just as you can show that an equation is false using correct mathematics (i.e. Given 4+A = 3+B and A>B, one is false), you can show that a set of premises is self-contradictory, and thus one false, by showing they can prove *anything*.
Later lessons allow you to just declare a contradiction. However, using only the rules of inference, this is how you show at least one premise demonstrably false.
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Thank you for your videos. I am not in your class but am taking an on-line class on logic and this helped me SO much. You are really great at breaking it down.
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OMG! I totally agree with you Pokerstud! He is soooo clear. I understood more in these past 6 mins than in the entire semester. My Logic Professor SUX. Kyphilosopher your GOOD!
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Man come to my university and teach... plz you just explained this whole process better in 6 min. than my current logic professor did all semester...
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d.f
hence d
hence g.h
hence g
hence~d
wtf?
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This seems logically false. First you have D in the affirmative, then you have the negation of D, in both instances they stand alone, which is a contradiction. I don't think that is correct. Can someone explain?
FrozenPondHockey 2 months ago
Natural deduction only establishes that an argument is valid. As can be shown by the truth table method, an argument is valid as long as there is no case where the premises are all true and the conclusion is false. This means that an argument with contradictory premises (one true and one false) will always be valid. however, such an argument cannot be sound since soundness requires actually true premises.
kyphilosopher 2 months ago