‘What is a circle?’ considers what is common to the objects that are circular. It is circularity, which to some is an example of a property: a feature or quality of a particular. But does circularity exist? Plato divided existence into two realms: the one we inhabit and the heavenly one where properties exist. How do these realms relate to each other? What if everything was a particular? This view is called nominalism, but this cannot deal with resemblance and leads to infinite regress. Aristotle's view — immanent realism — states circularity would be a real feature of the world but exist only in its instances: in circular things.