Is it possible to have a concept of X, without knowing the opposing concept not-X?

Attention Philosophers of 314!

Today, we examined this question:
"Is it possible to have a concept of X, without knowing the opposing concept, not-X? For example, is it possible to know happiness without knowing what unhappiness is?"

We had a very fruitful discussion - many issues and ideas were thrown up. Use this space to consolidate your thoughts and opinions, state any issues or ideas that continue to to plague you. If you have possible answers to your fellow philosopher's queries, do feel free to help resolve them :)

Have fun!