Everything we write or say has a point - we say it in a particular context for a particular reason. One of the things that we all had to learn was when, and how, to make the point crystal clear. That's what this column is about.
For instance, that last sentence could have been: "This column is about that." The meaning would have been correct, and - better still - it would even have been true, but it wouldn't have been so helpful to you. And the sentence before it could have been: "We all had to learn when, and how, to make the point crystal clear." Same comments: true, but unhelpful.
The interesting thing about these examples is that helpful grammar is complex. Here are the sentences again:
1. This column is about that.
2. That is what this column is about.
Sentence 2 takes two more words (is what) to give the same information, and yet you'll surely agree that it's more helpful.
3. We all had to learn when to make a point clear.
4. One of the things that we all had to learn was when to make a point clear.
In this case, the more helpful sentence 4 took six more words: "one of the things that ... was". And yet we're sure that these extra words were well used.
What these sentences do is to convert a statement into a kind of question-answer form. (There we go again: a simpler wording would have been: "These sentences convert a statement...") For example, sentence 2 asks what this column is about, and then answers it with that; and sentence 4 asks what we all had to learn before giving the answer. In other words, you start with the simple wording (sentences 1 or 3), and split it into two parts: question + answer. Grammarians call this process "clefting", and the result is called a "cleft sentence".
In slightly more technical terms, clefting takes one part of the simple sentence and turns it into a relative clause. Sometimes this is an ordinary relative clause, such as "(things) that we all had to learn". But it can also be a special kind of relative clause that can be used on its own without a modified noun, as in: "what this column is about". Either way, the relative clause sets up a question which is answered by the remaining part of the simple sentence.
Converting simple sentences to clefts and back again is a really useful classroom activity, as it focuses attention on the importance of context.
Start with: "Billy writes music." They offer: "It's Billy that writes music", "What Billy does well is write music", "What Billy writes is music." The class will learn flexibility - or rather, what the class will learn is flexibility.
Richard Hudson is emeritus professor of linguistics, University College London
Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk