Punctuation matters. There are two most frequently used types of punctuation in writing: A full stop and a comma. A full stop is quite obvious where to be put whereas a comma is often ambiguous. Therefore, here I make a note on the usage of commas.
English Punctuation - J. Morison
I found a book called 'English Punctuation' by J. Morison in the library and it looks good. Here are some quotes worth to take notes.
Commas between Clauses
1. Between Independent Clauses. Independent clauses are clauses that can stand alone as separate sentences without any grammatical connectives (such as conjunctions) but are nevertheless linked by sense or logic. Independent clauses can be treated as separate sentences, being separated by full points, as in:
I came. I saw. I conquered.
The cumulative effect of these statement is better seen, however, if they can be put into a single sentence. But how should we punctuate this sentence? The answer is to use commas:
I came, I saw, I conquered.
In choosing well-worn example, we have probably lighted upon the only general instance when commas between independent clauses are regarded as permissible - that is, the situation in which three or more independent clauses are linked together. We can justify it mainly on the ground that words or short phrases are in a list are separated by commas.
I think I would better avoid connect two independent clauses by commas at least in IELTS writing. It's too tricky. Let's move to other examples.
2. Between Co-ordinate Clauses. The use of 2 commas between co-ordinate clauses in sentence - i.e., clauses of equal status connected to each other by co-ordinating conjunctions such as and, but, for, neither, not, or, etc. - depends (in British English at least) on the length of the clauses, the closeness of the link between the clauses, and the writer's overriding duty to eliminate all ambiguity from the mind of the reader, however fleeting that may be.
On purely syntactical grounds, no commas are needed in the following plain statements:
John has bought a computer and is using it for work.
John has bought a computer but can only use it for work.
In these two sentences, both clauses share the same subject, and because the clauses are short, there is no need to repeat the subject or commute it to the corresponding pronoun.
The list of coordinating conjunctions are different from what I know. Here is my list: FANBOYS - for, and, nor, but, or, yet, so. These 7 conjunctions are commonly recognised coordinating conjunctions as I know. There is a link supporting my idea: http://www.chompchomp.com/terms/coordinatingconjunction.htm.
The key to remember here is that if the sentences are simple and short, then we don't need a comma.
Another quick note on one of the coordinating conjunctions nor. There are two rules to remember: 1) The first sentence must be negative (the negation can be implied). 2) The order of the subject and the auxiliary verb has to be reversed.
“Fenster doesn’t like to do his homework. Nor does he check his answers when he does do it.”
“Fenster turned in his math worksheet two days late. Nor did he check his answers before turning it in.”
The first sentence is an example for an explicit negative sentence while the second is implicit.
Let's go back to the original text.
When the subject is different, however, notions of contrast arise. Many writers under these circumstances, especially those in the United States, feel that a comma before the conjunction is required, as in:
John has bought a computer, and Jane has bought a typewriter.
John has bought a computer, but Jane is using it all the time for her word processing tasks.
Some British writers might balk at using a comma in sentences such as these, but a comma before a clause in which the matter is significantly different is usually essential:
Helen thought of herself as photogenic, but the camera doesn't lie.
He was dying to go out to the pub for a drink, and the dog obliged him by asking to be taken for a walk.
If you are seeking guidelines, the 'Change the subject, chuck in a comma' might not be a bad rule of thumb. Although not expressed in the most refined terms, it does have the important merit of being clear and consistent - something punctuation rarely is but always should be.
'Change the subject, chunk in a comma.' It looks a nice rule of thumb to remember. Then, of course, the real world is not that simple. Let's see what comes next.
Commas between co-ordinate clauses where subjects change are, however, not necessarily obligatory. At the risk of taking back our rule of thumb, we must concede that in the following examples, even though the subjects change, adding a comma is superfluous:
The band played and everyone danced.
Tessa sings quite well but Caroline is tone-deaf.
She agreed with them but I did not.
No commas are needed here for three very good reasons:
1. All the clauses are short.
2. They are closely linked with each other.
3. None of the sentences is likely to be misleading or ambiguous for readers.
In the light of all this we have to restate our rule of thumb relating to commas between clauses linked by co-ordinate conjunctions: 'Change the subject, chunk in a comma, but check for linkage, brevity and clarity first.'
Alright. There are more to remember but it is still fine. 'Change the subject, chunk in a comma, but check for linkage, brevity and clarity first.'
3. Between Main and Subordinate Clauses. Every normal sentence must have a subject and a main finite verb, a verb whose special distinguishing features - tense, mood, person, etc. - tie it to that subject.
Each of the following examples consists of a main clause followed by one subordinate clause. All are plain statements. None of them contains ambiguities, none of them poses a grammatical problem, so none of them requires any commas.
She left the office early that day because she was going out to the theatre in the evening.
I'd love to read that book when you've finished with it.
He said that he would come.
No commas are needed when two subordinate clauses follow the main clause, provided that each clause is dependent on the one before:
He said that he would come when he could.
John said that Jane could use his computer whenever she liked.
When more than two subordinate clauses follow a main clause, however, a comma is usually advisable:
John said that Jane could use his computer whenever she liked, as long as she was careful with it.
Here is the rule.
1. Main C. + Sub. C.: No comma.
2. Main C. + Sub. C. + Sub. C.: No comma again.
3. Main C. + Sub. C. + Sub. C. + Sub. C.: Then a comma before the last subordinate clause.
Since. A significant use of the comma in this connection is encountered in distinguishing between the two senses of since: the causal sense, in which since equals 'because' or 'for', and the temporal sense, in which since means 'during the period following the time when'. A comma is regularly used to signal the causal since; the absence of a comma usually indicates the temporal since. Thus the comma is essential in sorting out these two sentences:
I haven't seen her in London, since she got married last year. (causal)
I haven't seen her in London since she got married last year. (temporal)
Oh, I totally forgot this rule about since. Or I may never have learned it. It will help to memorise the rule by noting that both 'Causal' and 'Comma' start with 'C'.
Using a comma between a main clause and a following subordinate clause is generally restricted to the instances we have already described. When a subordinate clause precedes a main clause, a comma is much more likely to be used. But such a comma can be left out if the subject of both clauses is the same and especially if the subordinate clause is short. No commas are needed in these two sentences:
When he moved to Berlin he bought a flat.
Before I go I must tell you this joke.
But commas are needed in these:
Whether you like it or not, she will have to go.
As I told you yesterday, we have asked Smith to accept the position of chairman.
When John left, the house was all locked up securely.
If he dies, there will have to be a post-mortem examination.
In the last two examples, the comma is essential in stopping the reader from assuming at first sight that (a) the house is the object of the verb left, and (b) there functions as an adverb modifying the verb dies.
Sub. C. + Main C.: A comma is usually recommended to be used.
I didn't intend to write this long about commas. Well, let's just check one more thing.
Commas in Lists
Three or more items in a list of nouns and phrases in a series are normally separated by commas.
A musical sound is defined in terms of its pitch, duration, tone, colour and volume.
Among the stalwarts in the tenor section of the choir were Martin Miller, Tom Taylor, Michael Wright and Martin Hart.
Old boots, tin cans, cigarette packets, non-biodegradable sweet wrappers were all deposited in the entrance to the building.
The vexed question here is whether, in a cumulative list in which the last item is introduced by 'and' or 'or', a comma should be included or omitted before the 'and' or 'or'. The habit among British writers has generally been to omit, as in the first two examples just given. American writers, on the other hand, have tended to include the comma before 'and' or 'or', and it is hard to see why one should no do this. Where phrasal items in a list themselves contain conjunctions such as 'and' or 'or', a comma before the final 'and' or 'or' in the list is a mandatory aid to clarity. These examples show the recommended use of the comma in such lists:
Dostoevsky's greatest books include The Idiot, Crime and Punishment, and The Brothers Karamazov.
My favourite meals include bacon and eggs, fish and chips, steak, cheese on toast, and sausage and mash. Lovely!
I do not like peanut butter, chicken and ham paste, or mustard and cress in my sandwiches.
The habit among British writers has generally been to omit. Alright. I will forget about the Oxford comma.
The Oxford comma reminds me this video of Weird Al Yankovic. It's fun to watch.
I think this is enough about commas to successfully clear the huddle of IELTS writing.