An explication of two methods for proving invalidity in Predicate Calculus: the Counterexample Method, and the Finite Universe Method (100 Days of Logic)

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A description of Rule IV for validity for categorical syllogisms that negative conclusions must be drawn from negative premises and negative premises must illicit negative conclusions.(90 Second Philosophy & 100 Days of Logic)

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An explanation of the third rule of validity for categorical syllogisms, that at least one premise must be affirmative (90 Second Philosophy & 100 Days of Logic).

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A description of the Illicit Minor and Illicit Major Fallacies which break the second rule of validity for categorical syllogisms (90 Second Philosophy & Fallacy February).

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An explication of the conditionally valid categorical syllogisms of Figure 1 in Aristotelian Logic (90 Second Philosophy &100 Days of Logic)

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An explanation of how to determine if an argument is valid using truth tables.

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An explanation of the definitions of the terms Valid and Sound in Philosophy.

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