SD & SΔ: Two sides of the coin

Revised on 3/29/14

Malott’s definitions of S^D and S^Δ are procedural (see footnote on p. 199). They’re stimuli in the presence of which a reinforcement or punishment contingency is present or absent. This is different from the way some others define these terms. As Malott points out, some other definitions put the emphasis on either (1) the likelihood of the response happening in the presence of the stimulus, or (2) the likelihood that, if the response happens in the presence of the stimulus, it will be reinforced/punished. These two events – response happening and response being reinforced/punished – both depend on whether the reinforcement/punishment contingency is present or absent. This seems to make the presence or absence of the contingency primary and those two events are secondary.

An S^Δ is a stimulus in the presence of which the target response will not be reinforced/punished because the relevant contingency is absent. If there are no stimuli (circumstances, settings, occasions) in the presence of which the target response would not be reinforced/punished, then by definition there’s no S^Δ. This also means that the contingency is present all the time, so that there’s no particular stimulus “signaling” that the contingency is present. All of this is why Malott says that if there’s no S^Δ, then there’s no S^D.

The thing about coins is that they have two sides. There’s no such thing as a one-sided coin; you can’t have one without the other. And if you DON’T have one of them, then you don’t have the other either. That’s the way it is with S^Ds and S^Δs. If you don’t have an S^Δ, then you don’t have an S^D either (and vice versa, of course).