If you write the word “alligator,” the control is still thematic, even though the stimulus and the response product are now in the same mode (visual). The concepts of formal and thematic control play an important role in several aspects of the analysis that follows.
When a controlling variable evokes a response and has the following features:
There is NO point-to-point correspondence between the controlling variable and the response
Whether or not there is formal similarity between the controlling variable and the response
Formal characteristics of either the controlling variable or the response
Dynamic characteristics of either the controlling variable or the response