Was this for a Philosophy course? Some of my flatmates do Philosophy, but I'm more at home in the realm of numbers (I'm studying BSc Maths). I remember something like that happening to a friend of mine ages ago, just trying to remember the actual story of what happened. Vaguely similar to this, though... Anyway, if this is a question? Then this is an answer. But if this isn't an answer, then is this a question?
Basically, something we learned in Maths is that if one statement is true, it doesn't mean that it's converse (opposite) is also true. Like, you can say that all rabbits are blue, that doesn't mean that everything blue is a rabbit. However, you can also say that all fruits are an orange, and then say that all oranges are fruit (obviously these are hypothetical examples). That is a case where the converse is true. Sometimes it is, sometimes it isn't. Off-topic, I know, but an interesting point nonetheless...