Both a prompt and a probe may be either formal or thematic. If the source of stimulation has partial point-to-point correspondence with the response, then it is a formal prompt or probe, as in the case with echoic or textual stimuli.
A discriminative stimulus with the following features:
It is a supplementary stimulus
The person providing the supplementary stimulus can identify the response that the speaker is likely to emit
It is a supplementary stimulus
The person providing the supplementary stimulus cannot identify the response that the speaker is likely to emit
Whether the controlling relationship is formal or thematic
Who provides the supplementary stimulus (either another person or the speaker him or herself)