Table 2.

Definitions of mechanism (adapted from Mahoney [14])

	Definition #1—“Variables” (successionist mode)	Definition #2—“Theory of change” (successionist mode)	Definition #3—Scientific realism (generative mode)
Definition	An intervening (set of) variable(s) that explain(s) why a correlation exists between an independent and dependent variable	Frequently occurring causal patterns that are triggered under generally unknown conditions and with indeterminate consequences. A mechanism explains by opening up the black box and showing the cogs and wheels of the internal machinery. It provides a continuous and contiguous chain of causal or intentional links between the explanans and the explanandum	An unobserved entity that, when activated, generates an outcome of interest
Analytical approach	Correlational analysis techniques, such as mediation analysis, are used to identify “mechanisms” that are considered to be mediators of the observed effect	While slightly more broadly defined, this definition is compatible with probabilistic approaches to analysis	Causal analysis consists of identifying the configuration that links the outcome to mechanism(s) triggered by the context, often combining quantitative and qualitative data
Role given to theory	Theories in the form of universal laws can be deduced from empirical research (covering law principle)	Theories in the form of empirical knowledge derived from constant conjunction observations	Research contributes to developing theories of the middle range
Implications	Risk of reduction of mechanisms to measurable indicators, through which dynamic processes of change are reduced to correlations between variables that stand for more complex processes	In this view, and similar to definition 1, causation is reduced to the concatenation of elements in a causal chain. Causation is demonstrated to the degree that empirical regularities can identified	Empirical research allows investigation of a possible mechanism, thus identifying a plausible mechanism and may eventually lead to the identification of the actual mechanism. Research thus contributes to increasing the plausibility of the explanatory hypothesis