Why is C correct

Hi @filozinni, Thanks for the question! So let’s take a look at what the argument’s telling us. We’re told that many philosophers have argued that every person’s goal is to achieve happiness. And happiness here is defined as “the satisfaction derived from fully living up to one’s potential.” The philosophers also say that happiness is hard to get and takes years of sustained effort. But, says Deirdre, actually these philosophers are being too pessimistic and are wrong, since they’re making it seem harder than it is to be happy. After all, lots of people get happy feelings just from walking on the seashore on a nice, sunny afternoon. Now the argument asks us for a reasoning flaw in this argument. And we should notice something here: remember that when the philosophers are using the word “happiness,” they’re talking about “the satisfaction derived from fully living up to one’s potential.” But when Deirdre is talking about happiness, she talks about feeling happy from walking on a beach. Is this the same kind of happiness? No, she’s talking about something more fleeting, whereas the philosophers are talking about a much deeper sense of happiness. Walking on the beach, for the philosophers, wouldn’t make you happy, since it wouldn’t result in the satisfaction derived from fully living up to one’s potential. So Deirdre uses a different meaning of happiness (which is easier to get) to contradict the philosophers’ argument that happiness is hard to get, but they’re not talking about the same thing. (D) gets at this issue; the word “happiness” illicitly changes meaning over the course of the argument. Hope this helps! Feel free to ask any other questions that you might have.

Thank you very much @Shunhe!

You're very welcome!