Question

I know that illness is subjective, because the question of whether a person needs treatment is a subjective one. But what happens if the surrounding society thinks a person is ill while he thinks he is healthy? (Let’s say the person is insane.) According to what do we decide whether he is ill—by the society around him, or by what the person himself says? You can also split the question into a case where the person causes harm to those around him and a case where he does not cause harm.