Logic is simple. You need true premises. You can’t add anything on the way to the conclusion.

Logic is simple. You need true premises. You can’t add anything on the way to the conclusion. the premises must prove the conclusion. If the premise isn’t true, that’s a fallacy. If anything is added to the premises on the way to the conclusion, that’s a fallacy. Invalid forms add information on the way to the conclusion in sneaky ways. if the premise doesn’t prove the conclusion, something got added on the way to the conclusion.