Mastering Punctuation Marks: Comma, Period, Semicolon, and Colon Usage

The Comma (,)

The comma indicates a short pause. Use it in the following cases:

• To separate elements (words, phrases, etc.) in an enumeration, unless conjunctions like and, or, or nor are used. Example: I should need a PC, a printer, a modem, and a video.
• Before and after an explanatory or parenthetical phrase (an aside). Example: To obtain the full text of articles, you need only apply.
• Before, after, or before and after a vocative (direct address).
• To set off transitional phrases such as therefore, in contrast, i.e. (that is), etc.
• To separate clauses in a compound sentence, especially when using transitional adverbs. Example: God has all power (natural and supernatural) and is the creator of all things and, therefore, the right to everything.
• Whenever necessary to prevent ambiguity or improve the readability of the text.
• To separate items in a list where clarity is essential (e.g., the Oxford comma). Example: They will finance areas of Ecology and Environment, Economy and Finance, and Hospitality. (Note: Without the final comma, the name of each area might not be well-defined.)
• Between the integer part and fractional part in figures (in some conventions). Example: This year, investments have been 7,190,938.43 euros.

When to Avoid the Comma

Do not use a comma between the subject and the verb or between the verb and the complement, unless a parenthetical clause is present.

The Period (Full Stop)

The period (.) indicates a full stop or a long pause. Use it in the following cases:

• At the end of a complete sentence.
• Between hours and minutes when indicating time (e.g., 2.15 p.m.).
• To separate sections or subsections in numbering (e.g., 2.1.). Example: 2.1. The society and new technologies. (See page 1253 of the new Descriptive Grammar.)

When to Avoid the Period

Do not use a period after question marks (?), exclamation marks (!), titles, subtitles, or dates. Example: Hi everyone!

The Semicolon (;)

The semicolon indicates a longer pause than the comma but a shorter pause than the period (no space before the semicolon). Use it in the following cases:

• To separate independent clauses that are closely related in meaning but are not joined by a coordinating conjunction, or when the pause required is greater than a comma but less than a period.
• To separate items in a complex list where the individual items themselves contain commas. In this case, before the final element preceded by conjunctions (and, or, or nor), a comma is often used.

The Colon (:)

Colons indicate that the second element explains, illustrates, or elaborates on the first (no space before the colon). Use them in the following cases:

• To introduce a list, explanation, example, quotation, or conclusion.

When to Avoid the Colon

Do not use a colon if the sentence continues immediately after introducing a series of elements; in such cases, dashes or parentheses should enclose the subsequent clause. Also, avoid placing a colon where it breaks the grammatical continuity of the sentence (e.g., immediately following a verb or preposition).