With one exception, all actual entities for Whitehead are temporal and are (which are not to be confused with consciousness, or with mere subjectivity). This 'actual entity' idea is most distinctly characteristic of the metaphysics of "Process and Reality", and requires of the newly approaching reader a philosophically unprejudiced approach. An entity that people commonly think of as a simple concrete object, or that Aristotle would think of as a substance – a human being included – is in this ontology considered to be a composite of indefinitely many occasions of experience.