The problem with names is that they can always be applied to more than one thing. But the existence of unique individuals is self-evident. It is these two facts that create a puzzle for philosophers. Anything that can be applied in many cases is a universal. But something that is unique is a particular. But why should we believe in particulars at all if particular have nothing that makes them unique?
Any name at all can be applied to many things. This is not the claim that every name actually does apply to many things, but only that all names can potentially apply to many things. What seems to be strongest counter-example is names that we give for individual things themselves. The strongest example of these are personal names. So lets suppose that we know “Stephen”. He is a particular individual having a particular history. The name” Stephen” that I use applies only to him. But what makes this name apply to a particular individual? We know that Stephen could have had a different history. He might have been an only child, never attended university or lived in a different country. We might claim that it was necessary that he had the same parents, but this is nothing unique as I have the same parents as well. We might suppose that it is necessary that he have the particular genetic origins that he had. But if a had identical twin brothers with his genetic code, neither of them would be Stephen. (If one of them were, then which one is it?) So it seems that there is nothing about Stephen that makes him unique nothing that makes him distinct from a copy of himself.
Without his history, memories do not make him unique. Without his genetic code or other information, neither parents nor family make him unique. But if the very things that make him different from other human beings are not enough to make him unique, then what could make him unique. It seems that nothing at all makes him particularly different.
On the other hand, it is self-evident that particular things exist. The idea that no individual humans, forks, planets or dogs exist is absurd. Without individual things, there is no reason to believe in any universal at all. So rejecting the existence of particulars as such is irrational.
But these conclusions form a contradiction. If there is nothing at all that makes Stephen different from a copy of himself, then there is nothing that makes anything different from a copy of itself. Stephen is the preeminent example of a particular. If he is not really a particular, then nothing else is either. But it is self-evident that there are particulars. All self-evident sentences are true. Therefore, there are particulars. But then there both are and are not particulars.
Before continuing to examine this issue and come to a resolution, it is helpful to determine if this is the only problem with particulars and universals. This is problem with the existence of particulars. But there could be other kinds of problems. One of these has to do with the existence of universals.
I will discuss that problem next.