Choosing the right conjunction is important to make the meaning clear.
- He is intelligent but hardworking.
- He is intelligent and hardworking.
(Since the conjunction and connect similar ideas, it should be used in the above sentence.)
- I have always been weak in mathematics and I have never failed a test.
- I have always been weak in mathematics, but I have never failed a test.
(But is more appropriately used because the two sentences above have opposite ideas.)
When ‘and’ is used to connect two words or phrases in a sentence, no comma is used. Commas are used when there are three or more items in a sentence.
- I had bacon and an egg.
- I had bacon, a toast, and an egg.
We can start a sentence with a conjunction, or place it in the middle of the sentence. A comma is used when a conjunction introducing a subordinate clause comes before the main clause as shown here. The subordinating conjunctions are in bold.
- If he is not here soon, we shall leave without him.
- We shall leave without him if he is not here soon.
- When you see him, please talk to him about it.
- Please talk to him about it when you see him.
- Although she is my colleague, we hardly talk to each other.
- We hardly talk to each other although she is my colleague.
- Because the weather is bad, we decide not to go out.
- We decide not to go out because the weather is bad.
- Before I go to bed, I have a glass of milk.
- I have a glass of milk before I go to bed.
- After the accident, he decided to give up his job.
- He decided to give up his job after the accident.
(We use a comma when a conjunction introducing a subordinate clause comes before the main clause.)