Nominalism vs Realism

Realism [link]

At the foundation of philosophy is a question: what defines reality? There are several questions that are connected to this. Let us start with: when we say that a lot of different animals are all dogs, to what quality are we referring that makes the Dachsund and the Great Dane both dogs? Is there an essential quality of "dog-ness"? Some universal concept that is inclusive of all dogs, despite the particular differences between breeds?

There it is: universals and particulars.

Realism says that both universals and particulars exist. That is, we recognize that different dogs/houses/trees are those things because, although they have different particulars, there is a universal essence of dogs/houses/trees that exists. Plato and Aristotle were Realists.

Nominalism says that the world is made only of particulars. Things we see are put into categories by our thought processes and our language, not by the existence of some abstract universal. William of Ockham and Jean Buridan were Nominalists.

In the two diagrams shown, we see that in Realism, although John and David have different Particulars, they are defined by their Universal quality as human beings. Nominalism, however, shows John and David only defined by their Particulars. The category of Humanity is created by us. There is no abstract "Humanity" essence that exists independent of John and David.

Nominalism [link]

Getting at the truth produced some fascinating thought experiments. One—The Puzzle of Theseus' Ship—was posed by Plutarch (46-120 CE). The ship of Theseus was preserved in Athens for several generations. As pieces of it decayed, they were replaced with new wood, so that the ship would stay intact. If a thing is based on its particulars, then with the particulars of this ship having changed over the years, is it still Theseus' ship? If there is some universal of Theseus' ship (as Realism says) then it is still his ship. If there are only particulars (as Nominalism says) then it isn't.

British philosopher Thomas Hobbes (1588-1679) took this a step further: if all the removed pieces were assembled into a complete ship, then which is Theseus' ship? Are they both Theseus' ship? He concludes that this would be absurd.

Even the early scholars understood that there were problems with these concepts, and struggled to reconcile the issues. Still, they did their best to understand how reality worked, and how that would help them to understand everything else.

...such as whether we have individual souls. That discussion will take us back to Averroes tomorrow.