I'm studying for TOEFL and saw some punctuation rules online. Some sources mention the pause for comma, while others don't. Is there a canonical source for questions like this?
There are various ways to create pauses in sentences using punctuation.
The most common is the ","(comma), and tends to be the shortest pause.
There is also "-"(dash), "--"(em-dash), ":"(colon), and ";"(semicolon).
Commas often go where pauses would go, but I'd advise against using a comma simply to force a pause. Most credible guidelines I've seen caution against using commas where they shouldn't go simply because a reader might pause there.
For example, the Grammar Girl says: The “put a comma everywhere you’d pause” idea is an unfortunately common myth.
Another writing consultant opines: If you have a block of text that's so long it needs a mid-way breath while reading aloud, or if reading aloud leads you to throw in natural pauses to help structure the meaning, those are not necessarily indicators that the written text needs a comma.
And in the Writing Forward blog, Melissa Donovan writes: A comma often indicates a pause, but some pauses occur without any assistance from commas. In fact, one of the biggest mistakes people make is to simply place a comma wherever they want the reader to pause.
In addition to pausing, commas guide sentence intonation. Roughly, the comma separates groups of words that form a pattern of pitches. For example in a list, each item except the last has a rising pitch. The pattern of pitches within an intonation phrase is called the intonation contour.
English doesn't have enough punctuation to mark all the possible intonations. The comma can show where an intonation phrase ends, but it is up to the reader to supposes exactly how the expression should be expressed. The commas are a guide to prosody. By guiding the reader in how a sentence should be read, commas can improve clarity and reduce ambiguity.
A breath and a pause sometimes can occur at the end of a intonation group, but not always. The commas only guide prosody. They do not prescribe when and where to pause. Again in a list of short items, a speaker would not pause or breath after each item.
These intonation phrases often coincide with grammatical elements of the language, and so it is possible to use the grammatical structure of a sentence to deduce where commas should be placed, however they are not themselves part of the grammatical structure of the sentence.
There are notable dialectical differences in intonation between American, British and Australian.
If you're trying to write common speech patterns, the ellipsis […] is very common.
There are times when the length of your sentence can cause readers to have trouble following along, necessitating the use of a comma to break it up. The previous sentence is an example of such a case. Its purpose is to show where you would naturally pause while talking aloud.
However, sometimes it's better to just break the sentence up into two using a period. Use this method tactically when writing to help you vary sentence length. There are also other ways to break up sentences, including the semicolon and the hyphen. Ellipsis can be used to generate even longer pauses, but such a usage is typically considered informal.