Validity & soundness Validity = It cannot be the case that the premises are true and yet the conclusion is false Soundness = Valid + all premises are true

Female soldiers (1) Female soldiers have the skills and talent required for combat. Any soldiers with the skills and talent required for combat should be allowed to join a combat unit. Thus, female soldiers should be allowed to join a combat unit.

Female soldiers (2) Most female soldiers have the skills and talent required for combat. Major Susan Smith is a female soldier. Major Susan Smith has the skills and talent required for combat.

Pink elephants P1. All pink elephants on Mars own pet unicorns. P2. All pet unicorn owners vote Labour. C. Therefore, all pink elephants on Mars vote Labour.

Cats P1. All cats suckle their young. P2. All mammals suckle their young. C. Therefore, all cats are mammals.

A Colourless Green Idea P1: Colourless green ideas sleep furiously. P2: Who could disagree with that? C: Therefore, think that colourless green ideas sleep furiously.

Disarmament P1. If deterrence is not effective, then we should disarm our nuclear weapons. P2. Deterrence is not effective. P3. Nuclear weapons are extremely expensive to maintain. C. Therefore, we should disarm our nuclear weapons.

When formulating an argument… Use only declarative sentences; …make it valid, if at all possible; …do not add extraneous premises: ‘Every premise matters’

St. Thomas Aquinas “It seems that the existence of God cannot be demonstrated. For if His existence could be demonstrated, then that would be scientific knowledge. But our knowledge of God is through faith.”

Global Warming “Some people deny that man-made climate change is occurring. But these people have vested interests in making money by polluting the planet.”