A dog walking by may simultaneously increase the likelihood of saying “dog” and of saying “canine.” You may say both words on the same occasion or days apart. It may also increase the likelihood of the response “fur,” “German Shepherd” (if that is what it is), “brown,” “walking,” and others. Of course, it is typically the case that only one of these responses will actually be emitted, probably because several other controlling variables are also affecting it as we have just seen.
A situation with the following features:
There is a single controlling variable
That controlling variable simultaneously strengthens two or more different response forms
The specific type of controlling variable
The number of response forms which are strengthened
The type of elementary verbal relationship