I’m not going to lie. I think I would have grasped calculus a lot more easily, and perhaps even remembered it better, if it had been taught to me by starting with the actual meaning of the symbols instead of with all the jargon and symbols unconnected to the underlying concepts, as it used to be taught to 15-year-old American boys instead of not being taught to university graduates.
The preliminary terror, which chokes off most fifth-form boys from even attempting to learn how to calculate, can be abolished once for all by simply stating what is the meaning—in common-sense terms—of the two principal symbols that are used in calculating.
These dreadful symbols are:
(1) d which merely means “ a little bit of.” Thus dx means a little bit of x; or du means a little bit of u. Ordinary mathematicians think it more polite to say “ an element of,” instead of “ a little bit of.” Just as you please. But you will find that these little bits (or elements) may be considered to be indefinitely small.
(2) f which is merely a long S, and may be called (if you like) “ the sum of.” Thus fdx means the sum of all the little bits of x or fdt means the sum of all the little bits of t. Ordinary mathematicians call this symbol “the integral of.”
Now any fool can see that if x is considered as made up of a lot of little bits, each of which is called dx, if you add them all up together you get the sum of all the dxs, which is the same thing as the whole of x. The word “integral” simply means “the whole.” If you think of the duration of time for one hour, you may (if you like) think of it as cut up into 3,600 little bits called seconds. The whole of the 3,600 little bits added up together make one hour.
When you see an expression that begins with this terrifying symbol, you will henceforth know that it is put there merely to give you instructions that you are now to perform the operation (if you can) of totalling up all the little bits that are indicated by the symbols that follow.
That’s all.
If anyone is interested in Castalia re-releasing this early 20th century introduction to Calculus, let me know. Although I have to say, I think we’d lose the parentheticals, which are unnecessary and don’t help at all.