# Course:Phil150/deductivearguments

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.