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Sentence diagramming as an editorial tool: Commas with a series

Cat Haggert
Editors’ Association of Canada
(The Editors’ Association of Canada began using the name Editors Canada on July 1, 2015.)


Are you familiar with sentence diagramming? It can be a useful tool! As a copyeditor or a writer, you may rarely use sentence diagrams; but diagramming a difficult sentence often provides the clarity needed to apply grammar and style rules correctly.

What is a sentence diagram?

  • It is a pictorial representation of a sentence (like a map).
  • It shows what every word does.
  • It shows how words are related to each other.

Once a sentence is diagrammed, the words and their roles are clear, and grammar and punctuation rules can be compared to what is actually happening in the sentence.

This approach is useful in a variety of situations, including the following:

  • Ensuring subject/verb agreement
  • Making structures parallel
  • Changing passive to active voice
  • Capitalizing headlines
  • Punctuating a sentence

Rules for diagramming

An online search for "sentence diagramming guidelines" will provide many links to the basic mechanics of sentence diagramming. To diagram a sentence, it is helpful to have a dictionary handy. Other articles in the Language Portal will help you identify the parts of speech and brush up on your grammar. The following are the basic rules for diagramming a sentence:

  • The grammatical structure of the sentence is shown with connected lines that may be solid or dashed.
  • Words are placed on lines.
  • Capitalization is retained.
  • Punctuation is discarded.
  • Omitted (understood) words are added.

How can you use a sentence diagram to apply commas?

Comma use in English is regulated by many rules that apply in the following situations, among others:

  • Independent clauses
  • Adjective clauses (restrictive, non-restrictive)
  • Adverbial clauses
  • Absolute participial phrases
  • Items in a series

To show you how sentence diagrams can be used to apply comma rules, we have created some examples below illustrating the use of commas with items in a series.

Commas with a series of items

The comma rule related to items in a series is as follows: In a series of three or more words, phrases or dependent clauses joined by a single conjunction, a comma is essential between items not linked by a conjunction but is optional before the conjunction: e.g. "clapped, waved(,) and cheered." (The comma before the conjunction is known as a serial comma.)

However, when independent clauses are joined by a conjunction, a comma is normally used before the conjunction, regardless of the number of clauses.

Punctuate the following four examples correctly by (a) using commas (including the serial comma) to separate three or more items in a series, and (b) separating all independent clauses with commas.

  1. The rabbit looked at the fox dropped a load and ran.
  2. The other rabbit looked at the fox but froze in place.
  3. The detective decided to disguise herself follow the suspect observe him and arrest him.
  4. He left the room and she shut the door.

Diagramming these sentences results in the following:

Diagramming of the 4 sentences  Textual version below the image

On the basis of these diagrams, we can draw conclusions about the right way to punctuate each sentence.

  1. The correct punctuation is as follows: The rabbit looked at the fox, dropped a load, and ran.

    A comma is needed between the first two items. Also, the serial comma may be used before the conjunction "and" because there are three items in this series.

  2. The correct punctuation is as follows: The other rabbit looked at the fox but froze in place.

    That is, no comma should be added between two items joined by "but" unless they are independent clauses. It is clear from the diagram that "froze in place" is not an independent clause, because it is merely a second predicate sharing the subject "The other rabbit."

  3. The correct punctuation is as follows: The detective decided to disguise herself, follow the suspect, observe him, and arrest him.

    As can be seen from the diagram, the sentence contains a series of direct objects. The direct objects are themselves somewhat complex, each being a phrase made up of an infinitive (which is a verbal that can act as a noun, adjective, or adverb) and a direct object. A comma must be used between the first three items; and because there are four items, a serial comma may be used before the conjunction as well.

  4. The correct punctuation is as follows: He left the room, and she shut the door.

    In this case the conjunction joins two independent clauses. Independent clauses joined by a conjunction are separated by commas.