The document discusses the nature and definition of ideas. An idea is the intellectual representation of a thing in the mind, formed through senses, imagination, and abstraction. It exists universally in the intellect, is constant, and can represent immaterial concepts. In contrast, a phantasm is a sensible image that exists individually in the imagination and is changeable. Ideas have properties of comprehension, involving understanding of their meaning and containing intelligible elements that can be manifested through definition.