Answer:
If a deductive argument has all true premises and a false conclusion, then we know that the argument is invalid.
An argument is said to be deductive if the conclusion follows necessarily from the premises. In other words, if the premises are true, then the conclusion must also be true. If an argument has all true premises and a false conclusion, then it violates this principle of deductive reasoning.
Such an argument is said to be invalid, as it fails to provide a logically sound conclusion. It is important to note that even if an argument has all true premises, it is still possible for the conclusion to be false if the argument is invalid.