Edwin Abbott Abbott,
How to Write Clearly: Rules and Exercises on English Composition
“ The youngest pupils readily learn how to "expand a Metaphor into its Simile;" and it is really astonishing to see how many difficulties that perplex young heads, and sometimes old ones too, vanish at once when the key of "expansion" is applied. More important still, perhaps, is the exactness of thought introduced by this method. The pupil knows that, if he cannot expand a metaphor, he does not understand it. All teachers will admit that to force a pupil to see that he does not understand any thing is a great stride of progress. ”
