Joining ideas: conjunctions

conjunction

Words which join ideas together are called conjunctions. In English, conjunctions connect ideas. For example:
I went home and cooked dinner
I took a coat because it was cold
I looked for him but didn't find him
I don't have the money so I can't buy it

Examples in red on this page are wrong!

3 types of conjunction

Joining equal ideas

coordinating

These are called coordinating conjunctions. The ideas they join together can be in a different sentences and you still understand the meaning. The most important ones are but, so, and and or. For example:
It was raining. I didn't take a coat → It was raining but I didn't take a coat
It was raining. I took a coat → It was raining so I took a coat
It was raining. The wind was strong → It was raining and the wind was strong
It was raining or (it was) snowing all day

These conjunctions can only come between the ideas. You cannot say:
But I didn't take a coat, it was raining. That's WRONG.

Joining unequal ideas

These are subordinating conjunctions. You cannot understand one of the ideas without the other. The most important ones are because, if, although, before, after, when. For example:
    I took a coat because it was raining
    Take a coat if it is raining
    I didn't take a coat although it was raining
    It started to rain before I put on my coat
    I put on my coat after it started to rain
    I put on my coat when it started to rain

You can move these conjunctions to the beginning but you must use a comma, like this:
    Because it was raining, I took a coat
    If it is raining, take a coat
    Although it was raining, I didn't take a coat
    Before I put on my coat, it started to rain
    After it started to rain, I put on my coat
    When it started to rain, I put on my coat

Double conjunctions

correlating

These conjunctions always come together and join two ideas or two nouns. The most important ones are whether ... or, not only ... but (also), as ... as, both ... and (also), either ... or. For example:
    Whether it rains or it is sunny is not important
    Not only did it rain but the wind was very strong
    The weather is as bad today as it was yesterday
    Both the rain and also the strong wind made me uncomfortable
    Either it will rain or the sun will shine

With not only ... but also the grammar changes. You must make a question form after Not only.
Don't say: Not only it rained but the wind was strong.
Say: Not only did it rain but the wind was strong.

The meaning of conjunctions

Conjunctions do three main things:

Add things together: and, plus, not only ... but also, both ... and do this. For example:
I came on time and John was late
Not only was the weather cold but it was also raining
Both Mary and I want to come to the party and meet your friends
Give reasons: so and because do this. For example:
I will come early so I can help
Because it is raining, I'm not going out
Make an opposite idea: but and although do this. For example:
I was sure it was her but it wasn't!
Although she was unhappy, she smiled
Give different ideas: either ... or and whether ... or do this. For example:
Either he will arrive on time or he will be very late
Whether he comes or not is important