If it is true that Lincoln was killed in an automobile accident and it is true that IF Lincoln was killed in an automobile accident, then Lincoln is dead, then the conclusion that Lincoln is dead MUST be true. Lincoln was assassinated, not killed in an automobile accident. So, we have demonstrated a case in which a valid argument with a true conclusion is unsound. In other words, we have provided a counterexample to the statement in Exercise B14. No mental events are brain events.
All brain events are physical events.
So, no mental events are physical events. Try to use the visualization method to determine whether or not the argument is valid. If mental and physical events aren't your thing, then use the counterexample method as outlined in class. Be sure to create your own counterexample. No cats are otters.