Leibniz's analysis is this: when the causal state of affairs occurred, the relevant perceptions of substance x became more distinct, while the relevant perceptions of substance y became more confused.
Insofar as the relevant perceptions of x become increasingly distinct, it is "causally" active; insofar as the relevant perceptions of substance y become increasingly confused, it is passive.
GPs' perceptions of substance abuse were on a continuum from a chronic disease to a moral failing (for which the patient was completely responsible).
Therefore, affiliation with an older peer group putatively increases the risk for initiation and addiction because of greater availability of substances, peer modelling of use and biased perceptions of substance use norms.
Rather than thinking of compossibility in terms of the properties of substances, it might be easier to think of it in terms of the perceptions of substances.
From this, it should also be clear that the compossibility of substances in a world is another manifestation of Leibniz's thesis of the universal harmony of perceptions of substances.
Leibniz speaks of the "marks [les marques]" that each perception of a substance contains for all other perceptions that substance will ever have (Discourse on Metaphysics §8).
Most studies in the field have used data on the respondents' personal drinking or drug-taking to assess the actual prevalence, against which their perception of peer substance use has been compared.
The chemical behind this gustatory "hallucination" is a natural protein called miraculin, which temporarily coats your taste buds, altering the perception of sour substances for a few minutes.
