This is the fourth and final article of the series on how to use a comma. In this article, we talk about separating independent items in a series and independent adjectives with commas.

In this article, we explain how the comma is used to form certain grammatical constructions, including introductory phrases, transitional phrases, conditional clauses, and correlative conjunctions.

When a phrase forms a complete sentence, it’s called a clause. And like a non-restrictive (another word for independent) phrase, we use commas to show if a clause is independent.

To check if you need a comma, remove the phrase from the sentence, and if the meaning of what remains is unchanged, then it’s grammatically independent and needs a comma or two.

The format of abbreviations, in particular whether they end with a full stop or not, might seem a bit capricious. But the format of abbreviated words follows a fairly simple rule.

Always insert a space between an SI symbol and its number. The space is more than just a convention: it is a requirement of the international and Australian standards that govern the use of SI symbols.

Not starting sentences with "and" nor ending sentences with a preposition, such as “with” or “by”, are myths of grammar perpetuated by our schools. In fact, it’s good writing practice to start with “and” and end with “with”.

When forming possessives, it is a common misconception that the s is dropped for singular nouns ending with -s. Whereas, in most cases, the final s is retained, as in “Bridget Jones’s Diary”.

Also called a serial comma, the Oxford comma goes before the final conjunction ("and" or "or") in a series. It's not always necessary, but it is often essential to prevent misreading.

It’s time to move on. “Sulfur” (with an -f-) isn’t an Americanism: it was adopted as the international spelling over 30 years ago.

The abbreviation m is used as a suffix after a number (50m), and the SI prefix M is used before a unit of measure (50 Mt). They are not interchangeable.

Modal verbs, such as must, should and might, are some of the most grammatically complex parts of the language. Many have multiple meanings and are a common cause of ambiguity.