comma with 'not only X but' [conjunction]: not only clever, but also

[womble21]

When should I be using a comma in front of 'but'?

I can see no difference in these examples given in the same English grammar book, yet one has a comma preceding the 'but':
'She is not only clever, but also hard-working.'
'They tried but did not succeed.'

If there's a rule, does it apply to other conjunctions as well?

 

[jet_leader1]

'She is not only clever, but also hard-working.'
'They tried but did not succeed.'

In your examples, the use of commas is up to interpretation. As long as a lack of or the presence of a comma does not change the meaning of the sentence, you can choose to use it or not to use it.

Also, commas make sentences easier to read, since it separates a clause from another clause clearly.

-------

However, the use of the comma must be distinguished in the following examples:

1) The people, who roared in disgust, left the horrid performance after 3 minutes.

2) The people who roared in disgust left the horrid performance after 3 minutes.

In example 1, the commas show that everyone who was at the performance roared in disgust and left. Example 2 shows that only the people who roared in disgust, left the performance.

Do you see the difference?

 

[geoherb]

I would not use a comma in either of the sample sentences. A comma is necessary before but when it is introducing an independent clause--one that could stand on its own as a complete sentence. My old copy of the Harbrace College Handbook calls them main clauses instead of independent clauses. An independent clause has a subject and a verb.

She went to the movies, but he stayed home.
​

The rule applies to other conjunctions.

 

[Blue Spotted Frog]

Do a google search for the words "conjunctions" and "commas", and you will find a link at owl.english.purdue.edu that contains a lesson I remember from college -- that being:

A comma should precede a conjunction when there is an independent clause (complete sentence) on both sides of the conjunction.