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[wanderforlong-blog]

An argument is (deductively) valid if it is impossible for the premises to be true and the conclusion false; it is invalid otherwise.

forallx, an introduction to formal logic

In other words, a valid argument has three possible forms as below:

1. true premises, a true conclusion

2. false premises, a true conclusion

3. false premises, a false conclusion.

This thus means that an invalid argument contains true premises but a false conclusion.