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necessary and sufficient conditions
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 Related Terms
• rules of inference
• proposition
• hypothetical proposition


The question of necessary and sufficient conditions for something relates to how we evaluate arguments. A necessary condition for an event is something which is absolutely required to exist or happen if the event is to occur. An example of this would be the existence of oxygen for human life - without oxygen, we could not live. Therefore, the existence of oxygen is a necessary conditon for human life.

A sufficient condition for an event, on the other hand, does not have to exist for the event to occur, but if it exists, then the event will occur. To continue with our above example, the absence of oxygen is a sufficient condition for human death. Human death can happen without the absence of oxygen and does not require the absence of oxygen. However, if oxygen disappears, then people die. Thus, an absence of oxygen is a sufficient condition for human death.

A more formal way for saying that one thing, p, is a sufficient condition for some other thing, q, would be to say "if p then q," which is a standard hypothical proposition. Confusing necessary and sufficient conditions is one way to understand how some of the rules of inference with hypothetical propositions can be violated. The fallacy of affirming the consequent, for example, makes the assumption that a sufficient condition is also a necessary condition.

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What is the Logic and the Philosophy of Language?
The two fields Logic and the Philosophy of Language are often treated separately, but they are nevertheless close enough that they are presented together here. Logic is the study of methods of reasoning and argumentation, both proper and improper. The Philosophy of Language, on the other hand, involves the study of how our language interacts with our thinking.

What is Philosophy?
What is philosophy? Is there any point in studying philosophy, or is it a useless subject? What are the different branches of philosophy - what's the difference between aestheitcs and ethics? What's the difference between metaphysics and epistemology?

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