A teacher often faces difficulties and problems in communicating ideas and lesson to pupils in the classroom and outside. Many times pupils to whom she communicate, her ideas do not comprehend them properly. Sometimes they miss the point. She uses generally spoken or written words to communicate the messages.
She frames a mental picture of the ideas to be communicated in advance and translates that mental picture into words. This translation may take place ineffectively, with the result that only a part of the mental picture is transmitted as words. '
The pupil who listens to the words of the teacher imagines a mental picture of the ideas communicated by those words. The words he hears may not convey to him the some meaning which the teacher had put into them.
As Dale points out, "when we read a book, we do not take meaning out of the printed page, but put meaning into the printed page.' Therefore, when the teacher communicates ideas with the help of words, there is variation between the ideas communicated and the ideas comprehended in each step. This problem can be solved if the teacher uses other media of communication also instead of relying only on words. The other media are known as the “instructional aids".