More on SDs & SΔs

According to Malott, and just about everyone else as far as I can tell, the term, discriminative stimulus, is the "proper" name for the antecedent variable whose abbreviation is S^D. Its opposite, whose abbreviation is S^Δ, doesn't seem to have a proper name. Instead, we're usually told that the abbreviation stands for S-delta, which is really just a way of spelling out S^Δ that makes it clear how it should be pronounced and accommodates keyboards that don't know Greek.

In my opinion, discriminative stimulus should be the label for the category of antecedent variables that includes both S^D and S^Δ. In other words, there are two kinds of discriminative stimuli – S^Ds and S^Δs. An S^D is a stimulus in the presence of which a particular response will be reinforced or punished (depending on whether we're dealing with a reinforcement or punishment contingency), and an S^Δ is a stimulus in the presence of which a particular response will not be reinforced or punished.