A simple example, which illustrates the stratified nature of learning, is the fact that one has to learn to count before it becomes possible to learn to add and subtract. Suppose one tried to teach a child, who had not yet learned to count, to add and subtract. This would be quite impossible and no amount of effort would ever succeed in teaching the child these skills. The child must first learn to count, and only then does it become possible for him to learn to add and subtract. In the same way, there are things that a child must learn first , and only then does it become possible for him to learn to read, spell, write, et cetera.