I have trouble understanding the article on existence in this Philosophy dictionary.
Instantiation in reality, or actual being. Kant pointed out that existence is not a predicate.
What is the meaning of predicate in other words, put simply?
A predicate, from the Latin praedicare, which is itself a translation of Aristotle's κατηγορῆται, is something that is 'said of' something else. Thus in 'Socrates is bald', the predicate 'bald' is said of Socrates. To say that existence is not a predicate means that existence is not really said of any individual, i.e. is not a property of an individual in the way that being bald, being white etc are properties.
If it were a predicate, then 'Socrates does not exist' would be saying of some individual that he lacks some property, namely existence. But that is absurd: how can there be some individual such that there is no such individual? "Blue buttercups do not exist" is not saying that there are such things as non-existent blue buttercups. Rather, it is saying that no buttercups are blue.
Predicate is a fact about some thing or person, e.g.:
tall, a man and going for a walk are predicates about me. But in
(according to Kant) exist isn't a predicate, because if I didn't exist there wouldn't be me to apply the predicate to. Cf.:
Here I isn't someone at all, while in:
I is someone about whom it is told that she is not a man.
I thought to quote some parts from this helpful website that answers the question above. Beware that I do NOT quote all of the website, only the pertinent parts.
The following para discusses contemporary views, and departs from Kant's use of 'predicate'.