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.:
I am tall
I am a man
I am going for a walk
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.:
I don't exist
Here I isn't someone at all, while in:
I am not a man
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 Beware that I do NOT quote all of the website, only the pertinent parts.
According to Kant the confusion lies in the fact that existence is not a predicate. The predicate is that part of a sentence which is not the subject but which gives information about the subject. A predicate might be a single word like ‘John laughed’ where John is the subject and ‘laughed’ is the predicate. Or a string of words as in the sentence Clare went to school, 'Clare' is the subject and 'went to school' is the predicate. A predicate is a property that a thing can either possess or lack.
Predicates and the Existence of God
When people assert that God exists they are not saying that there is a God and he possesses the property of existence. If that were the case, then when people assert that God does not exist they would be saying that there is a God and he lacks the property of existence, i.e. they would be both affirming and denying God’s existence at the same time. Kant suggests that to say that something exists is to say that the concept of that thing is exemplified in the world. For Kant, existence is not a matter of a thing possessing a property i.e. existence. Existence is a concept corresponding to something in the world.
Kant's objection to the ontological argument is that existence is not a property that can be attributed to beings like we can attribute other properties such as being blue, hard, or round. When we talk about entities existing, Kant contends that we do not mean to add existence as a property to their beings. In other words, the objection seems to be that one cannot go around adding existence as a property to God (or anything else for that matter) in order to define God (or anything else) into existence. Unfortunately, defining my bank account as such a place that contains millions of pounds would not mean that a careful understanding of that definition of ‘my bank account’ would really make it so. In order to see if that definition were true, we would have to go to an ATM and check the balance of my account and see if it is accurate. Similarly, a definition of God must be checked with reality to see if it is correct.
The following para discusses contemporary views, and departs from Kant's use of 'predicate'.
So I separated it from the above because it's optional reading.
Contemporary Views of the Ontological Argument
Kant's objection has been very influential in the ontological argument debate. Philosopher are still divided as to whether or not existence is a predicate. Some thinkers controversially believe that existence can be thought of as a unique property. A modern advocate of the ontological argument is Alvin Plantinga (b.1932) Professor of Philosophy at Notre Dame University, USA. He has forcefully argued that Kant's objection does not conflict with anything in Anselm's argument. For Anselm does not contingently add existence as a property to God and define him into existence. Naturally these objections are contentious, which adds to the intrigue of the ontological argument.