Whitehead's Eight Categories of Existence
"There are eight Categories of Existence:
(i) Actual Entities (also termed Actual Occasions), or Final Realities, or Res Verae.
(ii) Prehensions, or Concrete Facts of Relatedness.
(iii) Nexūs (plural of Nexus), or Public Matters of Fact.
(iv) Subjective Forms, or Private Matters of Fact.
(v) Eternal Objects, or Pure Potentials for the Specific Determination of Fact, or Forms of Definiteness.
(vi) Propositions, or Matters of Fact in Potential Determination, or Impure Potentials for the Specific Determination of Matters of Fact, or Theories.
(vii) Multiplicities, or Pure Disjunctions of Diverse Entities.
(viii) Contrasts, or Modes of Synthesis of Entities in one Prehension, or Patterned Entities.
Among these eight categories of existence, actual entities and eternal objects stand out with a certain extreme finality. The other types of existence have a certain intermediate character. The eighth category includes an indefinite progression of categories, as we proceed from ‘contrasts’ to ‘contrasts of contrasts,’ and on indefinitely to higher grades of contrasts."
- Whitehead, Process and Reality, 22