To put it simply, an argument is valid when the premises lead to the conclusion without exception. On this test, we can assume that the premises we are given are true. Studying your sufficient and necessary reasoning is a great way to become familiar with what is valid and what isn't. It has to be rock solid reasoning with no loopholes. This is why it is so rare to have a perfectly valid argument. I'll give you a simple argument as an example:
Premise: All dogs are mammals. Premise: Jethro is a dog. Conclusion: Jethro is a mammal.
If we accept that these premises are true (which we must do on this test), then the conclusion is valid. Think of valid as guaranteed. If you are trying to determine if an argument is valid, try to think of a way around the conclusion. How could this conclusion be false?
It is hard to guarantee a conclusion in the real world, which is why we are often required to strengthen, weaken, and criticize arguments. Even when we strengthen an argument, it does not become completely valid/guaranteed. On must be true questions, we do have to select a valid conclusion.
I would pay close attention to the flaw in reasoning lesson. Mehran does 12 examples of the most common reasoning errors. This will help you to recognize an invalid argument.
