Philosophy / Unit 1 Philosophy 0027 short lesson, about 20 seconds
Necessary and Sufficient Conditions
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The idea
A necessary condition must hold for something to occur; a sufficient condition guarantees that it occurs.
In practice
Oxygen is necessary for fire but not sufficient. A lightning strike on dry brush is sufficient but not necessary.
Where people slip
Philosophical definitions typically aim at conditions both necessary and sufficient—which is why counterexamples bite so hard.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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