Comma rules explained, with examples

Reviewed by Benjamin Lohrer, editor at corrected.eu · Last updated: 9 August 2026

Commas: the most important rules

Comma errors are the most common kind of mistake in bachelor theses, in English and in German alike. Here are the most important English comma rules with examples and the typical errors, followed by a short section on how German punctuation differs. All the rules on this page are explained with examples.

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Commas: the quick decision

A comma mainly separates items in a list, an introductory clause from the main clause, non-defining relative clauses and parenthetical phrases. In a simple list, there is usually no comma before and or or in British English. Between two complete main clauses joined by and, but or so, a comma is normally set, especially when it makes the structure clearer.

For borderline cases, a good dictionary or a style guide is the authority. For academic work, follow the guide your university prescribes. The individual cases on this page translate the rules into concrete sentence patterns.

Commas in lists

A comma goes between the items of a list, but normally not before the final "and" or "or" in British English:

The serial comma (also called the Oxford comma) before the final "and" is optional. Many American style guides require it, British usage mostly leaves it out. Use it where it prevents confusion, and stay consistent within one text.

Comma after an introductory clause

When a subordinate clause (starting with although, because, when, if, while) comes before the main clause, it is followed by a comma:

When the subordinate clause comes after the main clause, there is usually no comma:

Commas with relative clauses

English distinguishes two kinds. A defining relative clause is essential to the meaning and takes no commas. A non-defining relative clause adds extra information and is set off by a pair of commas:

Commas with parenthetical phrases

Insertions are enclosed in commas, one before and one after:

Commas before coordinating conjunctions

When and, but, or, so or yet joins two complete main clauses, a comma normally goes before the conjunction:

No comma before "than" in a simple comparison

Common errors

• The comma splice: joining two main clauses with only a comma ("It was late, we left"). Use a full stop, a semicolon or a conjunction.
• Forgetting the comma after an introductory clause.
• Setting a comma between subject and verb ("The results of the study, show a trend").
• Forgetting the second comma after a parenthetical phrase.
• Putting commas around a defining relative clause, which changes the meaning.

Writing for a university? See our overview of spelling, grammar and punctuation. For comma questions, a professional final edit helps.

How German commas differ

If you write in German as well, or if German is your first language, the key differences matter, because German comma rules are much stricter and mostly structural. Where English commas often follow rhythm and meaning, German commas follow grammar.

• Subordinate clauses always get a comma, in front of and behind them, whatever their length: Ich weiß, dass das Thema komplex ist. ("I know that the topic is complex.") In English there is no comma before that.
• All relative clauses are set off by commas, defining or not: Die Studierenden, die regelmäßig kommen, lernen schneller. The English distinction between defining and non-defining clauses does not exist in German punctuation.
• No comma before the German words for "and" and "or" in a list, and a comma before "and" between two main clauses is optional: Er kam, und wir sprachen. or without the comma.
• Infinitive groups with "zu" may take a comma since the 2006 spelling reform, but need not: Es ist wichtig, regelmäßig zu lernen. The comma is recommended for long groups.
• Comparisons with "als" and "wie" take no comma in a simple comparison (Er ist klüger als ich.) but do when a full clause follows (Er ist klüger, als ich dachte.).
• The authority for borderline cases in German is the official rulebook of the Council for German Orthography (the Council's own German name is Rechtschreibrat), for everyday use the Duden.