The use of capitals varies greatly in different languages.

Attention will be mainly confined in this book to the usages followed in the printing of English.

Attempts to point out the various differences to be found in German, French, etc.

would only confuse the young apprentice.
These rules grow out of a fundamental principle.
The purpose of capitals is to emphasize the words in which they are employed.

With the exception of the cases of the words _I_ and _O_, which are capitalized for typographical reasons, this idea of calling special attention to a word, or words, for one reason or another will be found to be at the bottom of the variations in usage in different printing offices and by different writers.