existence

Recently I have been ponder about the meaning of "existence". No, I am not asking what the purpose of life is (which I consider a meaningless question). Rather, I am try to accurately define the meaning of saying "X exists."

When a person says "the table exists," I can understand this as an attribute of this table. The attribute "existence" in this case is true. However, I don't think this is reasonable: such an abstract attribute of an item (at least this is one way I understand "existence") also seems to be meaningless to me.

I think the real meaning of "existence" should be defined as subset operator. In other words, X exists if and only if X is a subset of the universe at a particular time. Existence is always a time-dependent boolean quantity. If anything is not part of the universe, then it is by definition non-existent.

Now if I press the question further: "how do I define the universe?" I can reuse the definition of physicality (previous post). Physical things are part of the universe. Physical things, because they interact with other physical things, are typically testable, though it may not be practical to test.

Still, I'm not exactly sure if this analysis is correct, but this is how far I have managed to achieve.