John Corcoran, at the State University of New York, writes that one of Ockham’s starting points is an
nominalistic ontology, a key principle of which is that a general term such as ‘animal’ denotes not a universal but rather each and every individual of which the term is truly predicable.
By pointing out that Ockham’s thought is “nominalistic,” we contrast Ockham with, for example, Plato, who thought that universals were independently existing objects. Plato thought that “blue” or “blueness” existed independently of any or all blue objects. Ockham, by contrast, writes that “blue” is merely a property or characteristic of blue objects, and has no being aside from actual blue objects. Ockham has a “lean ontology,” meaning that he believes that fewer things exist than Plato, who has a “rich ontology” - “ontology” being the study of what exists and what does not.
Building upon this first principle, Ockham talks about “supposition”:
According to Ockham’s terminology, a general term supposits for the individuals, if any, of which it is truly predicable.
So, for example, we can correctly substitute “a man” for the proper names John, Robert, and William in any sentences such as: “John eats pizza. Robert rides a bicycle. William reads a book.” This fact emphasizes Ockham’s nominalistic view that general or universal terms (like “man” or “blue”) are linguistic concepts - i.e., it’s all about the words - and not metaphysical concepts - i.e., not about actually existing things called “blueness” or “manhood” - and so the essence of the matter is revealed in the substitution in sentences, which keeps the center of the discussion of universals at the linguistic level, not the ontological level.
