What is Theatre?

We had a discussion in class about what exactly is theatre, and this furthered into what is a performance? The biggest controversy I saw was the way we looked at the idea of an audience and how that affected the definition of performance. In the discussion we decided that an audience would be defined as anyone including yourself. With this being said, I believe that anything and everything would be a performance. Because all though everything maybe not be intended to be performed or acted, there is always an audience present.

This idea of falling down the stairs was an example we used often. I personally think that even that would be considered a performance, because although no one has neccessarily seen it, you have been present, and since we defined an audience as anyone witnessing something, this fits. Here's how I see it:

Theatre is everything.
Everything is performed, and an audience is always present
because often you ARE the audience. For example, if you are lying.
While you are lying TO someone they are not aware of the lie.
So they are the audience, but the BIGGER audience is yourself
who knows that you're lying.
Even when something is not an act, it is still a performance
because I consider performances as anything that gets people to think.
so, if someone falls down the stairs, people are going to think "why did they fall down the stairs?"
or you will think "did i trip on something, why did i fall?"
If you're lying, that's an example of this too, because you think of the lie, which stimulates.