Imagine, if you will, a situation where a school board has decided that the children under their care are in need of special instruction. Naturally, they will consider carefully just what they want the children to learn before they begin to advertise for a teacher. They will want someone who can communicate to the children what it is they need to know, someone who can explain in language the children will understand the workings of a steam engine or the evolution of the pentadactyl limb. Not only that, however. The teacher will have to be able to show the children that they need to learn the subject in the first place. They will need to be persuaded that the knowledge is either useful or enjoyable, or at least that the consequences of not learning it will be rather uncomfortable.

It stands to reason, then, that the teacher must communicate with the children in their own language. Or does it? Take, for instance, the problem of learning a foreign language, say French. The school might imaginatively decide that they will employ a teacher who speaks only French in the classroom. The children may never have met anyone who did not speak their native language before. At first, they will be baffled, but they will quickly learn that if they want to communicate with the teacher, they are going to have to adopt a whole new means of communication.