Reasons :

Form

clause + conjunction + clause

It was raining so I stayed at home.

conjunction + clause + clause

Although it was raining, I went for a walk.

preposition + noun (phrase) + clause

Despite the rain, I went for a walk.

sentence + adverbial + sentence

It was a cold winter afternoon and the sky threatened rain. Nevertheless, we decided to go for a walk.

Reasons and results

Linkers are words or phrases that we use to link (i.e. connect or join) ideas.

It was raining. I stayed at home.

In this example, we can see that the first idea, 'It was raining.' is the reason for the second idea, 'I stayed at home.' Or, 'I stayed at home' is a result of 'It was raining.' We can use linkers such as so or therefore to make the relationship between the two ideas clear.

It was raining, so I stayed at home.

It was raining. Therefore, I stayed at home.

We could also change the order and put the result before the reason and use a linker such as because.

I stayed at home because it was raining.

The linkers so, because and therefore show a relationship of reason and result, or cause and effect.

Contrast

Let’s look at another example:

It was raining. I went for a walk.

This time there is a different relationship between the two ideas. People don't usually go for a walk if it is raining. The second idea doesn't normally follow from the first one. It is unexpected. This relationship, where the ideas are different or opposing, is called contrast.

We can use linkers such as but, although and however to show contrast and make the relationship between the ideas clear.

It was raining, but I went for a walk.

Although it was raining, I went for a walk.

It was raining. However, I went for a walk.

Comparing

Sometimes we want to compare two things that are different:

I always go to bed early.

My sister goes to bed very late.

This is also a kind of contrast and we can make the relationship clear using linkers such as while, whereas, but, however or on the other hand.

I always go to bed early, whereas my sister goes to bed very late.

I always go to bed early. My sister, on the other hand, goes to bed very late.

Adding points

One other common relationship between ideas is addition, when we want to add ideas. These can be very simple:

I like seafood.

I like spicy food.

We could add these ideas with linkers such as and, also and too:

I like seafood and spicy food.

I like seafood. I also like spicy food.

I like seafood. I like spicy food too.

In written English, we sometimes want to add ideas such as points in an argument. This is common when writing essays and reports:

The cost of relocation would be very high.

There are no suitable premises currently available.

A move would be unpopular with staff.

In formal writing we can join ideas like these with linkers such as furthermore, moreover, what is more, in addition and besides

The cost of relocation would be very high. Furthermore, there are no suitable premises currently available and a move would be unpopular with staff.

Note that simple linkers like and, too and also are often used in formal writing along with the more formal ones. But linkers such as moreover and furthermore are mostly used for more formal writing and would sound strange in simple conversation:

I like seafood. What is more, I like spicy food.

One sentence or two?

You will notice that we can link two ideas in one sentence or two. Your choice will usually depend on how complicated each idea is and whether you are speaking or writing. Simple ideas in spoken English are often joined with simple linkers like and, but, because and so:

I felt tired, so I went to bed early.

More complex ideas in written English are often joined in two sentences:

The disadvantages of relocating to a new site on the coast are considerable. Therefore we recommend retaining the existing premises in London for the time being.

When we link ideas in one sentence, each idea usually has a clause and the linker is usually a conjunction

The linkers and, but, so, while, whereas, and although are conjunctions and join ideas as clauses in one sentence.

The linkers however, on the other hand, therefore, furthermore etc. are adverbs and link ideas in two sentences.

Linking with prepositions

Some linkers are prepositions. They can link the same kinds of ideas as conjunction and adverbs, but the grammar is different. They don’t link clauses or sentences. They show a link between a word or phrase, usually a noun or noun phrase, and the whole sentence.

Contrast

We can use the preposition despite and the phrase in spite of (which works in the same way) to show contrast:

I went for a walk despite the rain.

In spite of her heavy cold, she managed to give a brilliant presentation.

Note that the ideas following despite (the rain) and in spite of (her heavy cold) are not clauses, they are nouns or noun phrases.

Reason and result

We can use due to and because of (not because) in the same way:

Due to the terrible weather we have cancelled the picnic.

Note that the idea following due to (the terrible weather) is a noun phrase.

Addition.

Besides can be used as a preposition to add ideas (it can also be used as an adverb).

Besides the problem with transport, we also had to deal with a difficult financial situation.

Note how the idea following besides (the problem with transport) is a noun phrase.

Other ways of linking and other relationships

Be aware that there are other ways of linking ideas in English. These are just some of the more common ones.

There are also other relationships between ideas, not just those mentioned here.