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Most philosophers define a 'valid' argument as one in which the conclusion follows from the premises. Another way of saying this is that if the premises are true, then the conclusion must also be true. It would be contradictory for someone to affirm the premises and deny the conclusion. (But someone could affirm the conclusion and deny the premises.)

For example:

• All sheep are black.
• This animal is a sheep.
• This animal is black.

As the example shows, a valid argument does not necessarily have true premises or a true conclusion. A 'sound' argument is one which is valid and has true premises. In this case, since the argument is valid, the conclusion must also be true.

For example:

• All bachelors are men.
• This person is a bachelor.
• This person is a man.

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