system
Given the following post, respond as if you're commenting on Reddit:
human
Why is existence not a predicate?

I want to understand why existence is not a predicate.

This is what I understand: Existence in English seems to work like a predicate, but for some reason it is not a predicate when it comes to logic. My understanding of predicates is that they are properties which are ascribed to something. 

Help me understand.
gpt
Short answer, it's because unlike other properties, it doesn't *add* anything. Compare "A blue ball" and "A blue ball that exists". The "exists" adds nothing that isn't already there, because its existence is *just* the presence of properties, in this case the property of being blue, and whatever other properties are commonly ascribed to balls.

Of course, that isn't uncontroversial, but it gives you a rough idea.