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Deductively valid argument: IF the premises of the argument are true, then the conclusion must be true. The validity of an argument does not depend on whether the premises are actually true.

Example of a deductively valid argument with true premises: (Katie Reeder)

1. If it is Monday, Vanier cafeteria has stir-fried Tofu
2. Today is Monday
3. Vanier Cafeteria will have stir-fried Tofu.

Example of a deductively valid argument with false premises: (Benjamin Sidloski)

1. Humans are carnivorous insects. 2. Margaret is a human. 3. Therefore, Margaret is a carnivorous insect.

Example of a deductively invalid argument (fallacy of affirming the consequent): (Vaibhav Sokhi)

1. If shape X is a square, then shape X is a rectangle.
2. Shape X is a rectangle.
3. Therefore shape X is a square.

Written in propositional logic:
1. If P then Q.
2. Q.
3. Therefore P.