Proponents of the GH avoid explicit assertions regarding causality (“causal claims in the Gateway Hypothesis . . . are still beyond reach” (Kandel and Jessor, 2002, p. 371)). Nonetheless, causation is implicit in the statements such as “one licit drug is required [emphasis added] to make the progression to marijuana use” (Kandel and Yamaguchi, 2002, p. 71), or “[t]he use of a drug at a lower stage is necessary [emphasis added] but not sufficient for progression to a higher stage indicating involvement with more serious drugs” (Kandel and Yamaguchi, 2002, p. 69). It is also stated that the validity of the GH is based on (1) the sequence of drug use initiation, and (2) “association in the use of drugs, such that use of a drug lower in the sequence increases the risk of using drugs higher in the sequence. Ultimately, association implies causation if all possibilities for spurious associations have been eliminated.” It is only because of “the difficulties of establishing true causality in the social sciences” that “the term association rather than causation is emphasized . . .”
