In part because of these issues, that levels in psychiatry are not Marrian, Campbell (2006) argues for an interventionist approach to causation. This is the view that when we say X is a cause of Y we are saying that intervening on X is a way of intervening on Y (Woodward and Hitchcock 2003, Woodward 2003, Pearl 2000): manipulating one variable makes a difference to another. This is not a reductive analysis of causation, since it makes use of causal ideas—it just states that questions about wheth