https://maximummathematics.com/books/foundational-mathematics/proof/invalid-arguments/index.htmlAll of us have, at one point, been presented with an argument that doesn’t seem quite right. Just because someone can string together a group of premises and assert some conclusion doesn’t mean that conclusion actually follows from the premises. Remember that an argument is valid if the argument’s implication is a logical implication — meaning that no matter what truth values the argument’s propositions have, the overall implication always evaluates to $1$. This means that if we can come up with even one truth value assignment reducing to the form $1 \to 0$, the argument isn’t valid. In other words, for any argument $(p_1 \land p_2 \land \dots \land p_n) \to c$ with $c = 0$ (and all premises true), the argument is invalid.Hugoen-US