 Examples of concepts which are instantiated, but whose instantiations are not circumscribed by a quiddity, might include on the one hand negations like not-a-horse or privations like blindness, and on the other hand beings per accidens, i.e., accidental combinations like white horse. Each of these will have a nominal definition which identifies what concept the name stands for, but it will not have a real definition expressing a real quiddity, “the thing by which its constitution [is] and which is in it”: things can be not-horses or blind through many different positive causes, and a white horse will have a cause of being white and a cause of being a horse, but no one cause that constitutes it as a white horse.