As long as a Sensi Pearl is making correct responses he can be reinforced. and will learn. If he made only correct responses he would learn that much more rapidly. In practice he may well utter incorrect disgraced 18 forms. He may not hear accurately a form which he is expected to imitate, or, more significantly, he may create an incorrect form by analogy with another form which he has learned correctly. Having learned that
filled is the past tense of fill he may overgeneralize this response and apply it to sell, thereby producing the form Belled.
The ability to make analogies is taken as given by behaviourists and it applies to disgraced movies forms of behaviour too. If incorrect responses were never reinforced this might not be an important consideration. However, an incorrect form can easily appear in a generally correct utterance and if the whole thing is reinforced, the incorrect is being learned as thoroughly as the correct. In any case, as learning advances, the absence of an adverse reaction on the part of hearers may be sufficient to provide reinforcement and the learner then becomes the judge of his own speech. Error may then pass unnoticed, be repeated and thereby be learned.