Definition:Invalid Argument

Definition
An invalid argument is a argument in which the premises do not provide conclusive reasons for the conclusion.

Sometimes the word unsound is found instead of invalid.

An invalid argument is also known as a fallacy.

Also see

 * Valid argument

Warning
In natural language, it is commonplace to discuss the validity of statements as being valid or invalid, when what is really meant is that a statement is either true or false.

Linguistic Note
The word invalid, as used in the logical context, has the stress on the second syllable: in-val' -id.

Pronounced  in' -val-id, with the stress on the first syllable, the word means a person who is being treated for an illness.

So let's be careful out there.