  Labels aside, several versions of the premise appear in the literature, and they can differ in strength. Note that the principle as formulated says nothing about whether the non-physical can affect the physical; a strengthened version prohibits this. (Closure is sometimes reserved for this stronger principle: LePore and Loewer 1987; Kim 1998, p. 40; Marcus 2005; compare Strong Causal Closure in Montero 2003.) An even more ambitious version blocks the non-physical from being cause or effect; such is suggested in Davidson’s work (see §5.1 and McLaughlin 1989, who uses Physical Comprehensiveness for this thesis.) As for weaker versions, Completeness could be limited to physical effects within the human body without affecting its relevance to the current topic. Note also that the principle is apparently committed to deterministic physical causation; a weakened version permits probabilistic causes. (For complications with such a weakening, see Montero 2003, and for other challenges with formulating Completeness, Lowe 2000; Gibb 2015.)