10. Common nouns and adjectives often begin with capital letters when they designate the topics or main points of definitions or similar statements. Such capitals are called emphatic (or topical) capitals.
Note. Emphatic (or topical) capitals are analogous to capitals in the titles of books (see Rule 7), but their use is not obligatory. They are especially common in text-books and other elementary manuals.
RULES OF PUNCTUATION[68]
The common marks of punctuation are the period, the interrogation point, the exclamation point, the comma, the semicolon, the colon, the dash, marks of parenthesis, and quotation marks. The hyphen and the apostrophe may be conveniently treated along with marks of punctuation.
I
1. The period, the interrogation point, and the exclamation point are used at the end of sentences. Every complete sentence must be followed by one of these three marks.
The end of a declarative or an imperative sentence is marked by a period. But a declarative or an imperative sentence that is likewise exclamatory may be followed by an exclamation point instead of a period.
The end of a direct question is marked by an interrogation point.
An exclamatory sentence in the form of an indirect question is followed by an exclamation point; as,—“How absolute the knave is!”
2. A period is used after an abbreviation.