Gregory begins with a defense of his position that children possess the innate ability to think, which I will simply assume and not summarize. If you aren’t sure if your children are able to think, you’ll have to read that part yourself.The law of the lesson has its reason in the nature of the mind and in the nature of human knowledge.
Nature of the Mind — The mind connects thoughts through graded steps and linked facts; each mastered idea is equipment with which to continue on in “fresh advance.”
Nature of Human Knowledge — Knowledge is organized and connected inherently; it is not simple and independent loose facts: “Each fact leads to, and explains, the new. The old reveals the new; the new confirms and corrects the old.”
So, in teaching, our goal is to lead the student by such gradual steps that the pupil “who has mastered one lesson knows half the next.”It is a serious error to keep the studies of pupils too long on familiar ground under the assumed necessity for thoroughness.Only deeper understanding, new lessons, should be sought when covering old material. Yet, you must also have mastery of the old before you proceed to the new:Imperfect understanding at any point clouds the whole process.Of course, we must also keep in mind that “mastery” is a relative thing, for no man actually possesses true and complete mastery of any subject or skill. So, what we are seeking is wisdom in our own particular situations with our own particular charges. The best way to teach new through old is through metaphor, for all figures of speech “are but so many attempts to read the unknown through the known.” Metaphors are attempts to flash light from the old upon the new. Each person tends to use objects and language and concepts from his vocation as his metaphor-light, as his familiar key to unlock or grasp the mysteries of that which is unfamiliar. Be aware of this and try to use metaphors of the children’s world and not of worlds they do not know (this is the law of language again). The difficulty in answering children’s questions lies not in the complexity of the question or the answer, but in the children’s lack of experience and vocabulary you can draw upon to explain.