You have gone through two years of medical school but are suddenly wondering whether you would be happier as a musician. Which of the following statements are potentially valid arguments and which are not?

a. “I can’t give up now, after all the time and money I’ve put in.”

b. “If I had thought about it from the beginning, I never would have gone to med school, so I should give it up now.”

c. “I wasted two years, but never mind — let’s start from here.”

d. “My parents would kill me if I stopped now.”