[robertpaulsen]

"I'll consider taking up the question if you promise to swear off lecturing everyone else on submitting pie-in-the-sky hypotheses."

I'll withdraw that question in favor of the other. If Substance A was legal, are you saying we'd see no change whatsoever in the use of Substance B?

[tacticalogic]

If Substance A was legal, are you saying we'd see no change whatsoever in the use of Substance B?

No, I'm saying that we'd see no change in the pre-disposition to use Substance B. If whatever is causing the pre-disposition to want to use Substance A also causes a pre-disposition to use Substance B, legalizing or criminalizing Substance A is not going to change whatever is causing the pre-disposition.

[ThinkDifferent]

If Substance A was legal, are you saying we'd see no change whatsoever in the use of Substance B?

Presuming A and B are partial substitutes, if A were legalized (i.e. made cheaper), demand for A would increase and demand for B would decrease.