Exemplification can be found in ontologies from the ancient world, such as those of Plato and Aristotle, and more recent ontologies, in particular those that take what exists to be determined by the empiricist's Principle of Acquaintance. This study examines some of the ways in which exemplification takes different forms in these different ontologies. Exemplification has also been criticized as an ontological category. This paper examines a number of these criticisms, to see the extent to which they are viable.