What Makes an Argument Valid
An argument can be valid and still have a false conclusion, and it can reach a true conclusion by luck. Separating the shape of the reasoning from the truth of the parts is the first move in philosophy and in every argument after it.
What a learner can do afterwards
- Set out an argument as premises and a conclusion, in your own words
- Give an example of a valid argument with a false conclusion and explain why it is still valid
- Say what has to be added to validity to get soundness
1 · Read
Every argument has two parts. The premises are the reasons offered, and the conclusion is the claim they support. Watch for signal words. So and therefore point to a conclusion, while since and because flag premises. Writers hide the shape, so your first job is to lay it out: premise one, premise two, therefore conclusion. Only then can you ask whether it holds up.
Validity is a narrow promise. An argument is valid when the conclusion must be true if the premises are true. That is all it promises. Try this one. All cats can fly. Mittens is a cat. So Mittens can fly. If those starting claims were true, the ending would have to be true. The link holds even though the start is nonsense.
Truth and logic can split either way. Take two true claims plus a true ending they do not support. The battle of Hastings happened in 1066. Tamaracks are deciduous conifers. Therefore Paris is the capital of France. All three lines are true, yet the reasoning is empty. Now flip it. If the moon is made of cheese, then mice vacation there. The moon is made of cheese. So mice vacation on the moon. False from start to finish, but the step itself is airtight.
Add true premises to a valid link and you earn soundness. A sound argument is valid with true starting points. Also watch the most common broken link. If it snows, schools close. Schools closed. So it snowed. Other causes close schools too, so the ending does not follow. To test any link, assume the premises are true and ask whether the conclusion could still be false.
Validity checks the link from reasons to claim, and adding true starting points turns a valid argument into a sound one.
2 · Watch
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Where it sits
Learn first
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.