Physics (not the kind one throws to the dogs, of course) is then subdivided into Astronomy, Chemistry, and Geology, while Biology has its two great divisions, Zoology (animals) and Botany (plants), all these having subdivisions reaching into every ramification of the material universe, which is the real subject matter of science, being as it is the only thing about which we possess any “knowledge.”
Another way of learning to classify is to select a subject and then “read it up.” Here is a good method:
Take a ten-cent copy book, the usual size about eight by six inches and begin on the first inside page. Write on the top of the page, left side, a good subject, leaving that page and the one opposite to be used for that question. Turn over and do the same again on the next page with some other subject. This practice of selecting subjects, in itself, will be valuable training.
In the search for subjects take any good lecture syllabus and select those about which you have a fair general idea. You will soon learn to frame some of your own. Good examples of standard questions are “Free Will,” “Natural Selection,” “Natural Rights,” “Economic Determinism,” “Mutation,” “Individualism,” and a host of others, all of which have a distinct position in thought, and about which there is a standard literature.
Then, in your general reading, whenever you come across anything of value in any book, on any of your listed subjects, turn to the page in your copy book and enter it up, author, volume, chapter and page. When you come to lecture on that question, there it will be, or, at least, you will know just where it is.
Of course, the two pages devoted to “Natural Rights” would mention, among other references, Prof. David G. Ritchie’s book on “Natural Rights”; and the eighth essay of Huxley’s First Volume of “Collected Essays,” in which he annihilates Henry George.
All this means an immense quantity of reading, but unless you have carefully read and weighed about all the best that has been said on any question, your own opinions will have no value, and it is simply presumption to waste the time of an audience doling out a conception that, for aught you know, may have been knocked in the head half a century ago.
What can be more tiresome than the prattle about “absolute justice,” “eternal truth,” “inalienable rights,” “the identity of the ethics of Christianity with those of Socialism,” and a lot of other theories, which lost their footing in scientific literature and transmigrated to begin a new career among the uninformed, sixty years ago.
Of course, some of these positions look all right to you now, but when you learn what has been revealed about them by the science and philosophy of the last six decades, they will seem about as rational as the doctrine of a personal devil or the theory of a flat earth.
And until your reading is wide enough to give you this view of them, you had better not attempt course lecturing in the twentieth century.