Apart from these refutable assertions, it is hard to discern a falsifiable, i.e., hypothetical, element in the GH beyond the sequence observation. Virtually every proposition of the GH is qualified by a disclaimer, effectively engulfing and neutralizing possible arguments to the contrary. Indeed even the core facet of the GH is hedged: “[t]he notion of developmental stages in drug behavior does not imply, however, that these stages are either obligatory or universal, nor that all persons must progress through each in turn” (Kandel, 2002a, p. 3) (cf. the above quoted contradicting statements of necessity to pass a “lower stage” and the requirement for using of a licit drug to progress to marijuana). After decades of research, even “[t]he notion of a Gateway drug itself is vague” (p. 7).
