A «Phase» is a kind of «Facet» that is a state of an identifiable thing that changes over time. For example, Living and Deceased might be phases of an Organism; or Egg, Larva, Pupa, and Adult might be phases of a butterfly.

When the necessary conditions for a «Phase» concept are met, which may include the occurrence of an event or meeting a condition, such as having wings, the identifiable thing will be a member of that «Phase» concept.