Suppose you are aware of two facts: Fact A. I feel tired.
Fact B. I have a cold.
And suppose you think that the cold is the reason for the tiredness. One grammatical option is to leave the causation implicit: I feel tired. I have a cold. Sometimes this is enough. After all, you must have some reason for putting these sentences next to each other, so the hearer looks for a connection; and "common sense" does the rest. In this case, common sense is the shared knowledge that colds cause tiredness.
In some cases, though, you need to be more up-front about the causation. There are surprisingly many grammatical options to choose from: I have a cold. I therefore feel tired.
I have a cold. That's why I feel tired.
I have a cold so I feel tired.
I feel tired as I have a cold.
As I have a cold, I feel tired.
I feel tired because I have a cold.
Because I have a cold, I feel tired.
Having a cold, I feel tired.
I feel tired because of my cold.
My cold makes me feel tired.
All of these sentences and sentence-pairs describe the same situation, but each presents it in a slightly different way.
The earlier sentences in the list present the cold and the tiredness as equals, but by the bottom of the list the cold is clearly subordinate and more or less taken for granted. Yet other options allow us to downgrade both the cold and the tiredness so that we can focus on the causation: It's because I have a cold that I feel tired.
My cold is the reason for my tiredness.
Every one of these grammatical alternatives has its own distinctive contribution, and deserves a place in any writer's tool-kit; but it's important to be aware that they all express exactly the same causal connection between the cold and the tiredness.
These varied ways of linking cause and effect help writers to express ideas with more precision and subtlety.
A good classroom activity is for students to explore how these different techniques work in different types of writing, from informal letters to formal scientific reports. In the process they will be developing their writing skills by making explicit some of the many options they have as writers.
Richard Hudson is professor of linguistics at University College, London Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk