 Serious actualism—also known as property actualism (Fine 1985), the (modal) existence requirement (Yagisawa 2005; Caplan 2007) and the being constraint (Williamson 2013: §4.1)—is a substantive logical and philosophical issue. However, as it is for the most part a domestic dispute among actualists, it is largely orthogonal to the possibilism-actualism debate proper. Consequently, it will not be pursued here in any greater depth. For further discussion in addition to the references above see Plantinga 1985 (which contains replies to Pollock and Fine), Salmon 1987, Menzel 1991 and 1993, Deutsch 1994, Bergmann 1996 and 1999, Hudson 1997, Stephanou 2007, Hanson 2018, and Jacinto  2019.[50]