Determination that an individual identified in one way is numerically identical with or distinct from an individual identified in another way (e.g., Venus, known as the morning star in the morning and the evening star in the evening). Since the concept of an individual seems to require that it be recognizable as such in several possible situations, the problem of individuation is of great importance in ontology and logic. The problem of identifying an individual existing at two different times (transtemporal identity) is one of many forms that the problem of individuation can take: What makes that caterpillar identical with this butterfly? What makes the person you are now identical with the person you were a decade ago? In modal logic, the problem of transworld individuation (or transworld identity) is of importance because the standard model of theoretic semantics for systems of modal logic assumes that it makes sense to speak of the same individual existing in more than one possible world.