Being Is A Predicate

Probably the most well known objection to St. Anselm's Ontological argument, usually attributed to Kant, says that existence is not a predicate. When we inquire into the nature of things, we say that it is this shape and that color, and these statements have some meaningful content to them because we are able to predicate something to them. They tell us something about the object. However, saying that X exists tells us nothing about the nature of the object. So being is not a predicate. 

This is not the view of the scholastics, and definitely not the view of St. Thomas Aquinas, who does say being (or existence) is a predicate. So how then do we deal with the above objection? Let's look at the mode of inquiry. When we ask what something is, we answer by giving a more common term to which we add a specific difference. So when we ask what a cat is, we say it is a mammal that has this or that distinguishing feature. We may ask what this more common thing is as well, and we answer with a more universal term. So if we were to ask what a mammal is, we say that it is a warm blooded vertebrate. But this line of questioning cannot go back into infinity. There must be something which is not known through anything else, but is immediately evident to the intellect, and this is being and is the prerequisite for any investigation into reality. All other conceptions are additions to being. There is a difference between being simpliciter and being in a certain sense (ens simpliciter vs secundum quid). Being a mammal is being in a certain sense since this act is added to something already actual.

So when we ask, is existence, or being, a predicate, we answer yes, but it is not a secondary thing like we consider all other predicates. It is prior to all other predicates in order for the thing to exist and our inquiry to begin at all. Because people don't make a distinction between the two, they erroneously think existence is not a predicate.