Pay attention to the subordinate clause: "your name was John". Taken out of context it looks very odd because people's names don't change, so we expect the present tense: "Your name is John". How come we use a past-tense verb to talk about something which is still true? Answer: it's the effect of backshift: the tense is shifted back to fit the time of the thought (I thought) rather than the time of the situation described (Your name is John).
This trick comes in handy because by shifting the tense we also shift the responsibility for the thought concerned. So we can easily follow "I thought your name was John" with "but I've now remembered you're Fred".
This is something we all do in ordinary speech, so it's not news to a KS3 writer, but of course few of us could put the rule into words. We may all be expert backshifters in speaking, but writing is another matter. There are two differences that matter here: it's more conscious, and it's slower.
If we use an over-simple view of tenses, KS3 writers may struggle.
In class it's tempting to squeeze tense into a rather predictable formula: present tense for situations in the present, and past tense for situations in the past. The trouble is that this doesn't do justice to what any KS3 speaker actually knows (deep down); for example, it ignores backshift.
Result: the writer is faced with a choice between instinct (backshift if the thought is in the past) and instruction (use the present if the situation is in the present).
The other problem is speed. For a novice, writing is much slower than speaking so it's harder to carry out long-term plans. One of the useful features of backshift, in the hands of a skilled writer, is the way it helps us to understand literary effects: "Bill knew honesty was important.
Lying always ended in tears, and however painful it might be, the truth was always better." And so on. We know from the past tense of "ended" and so on that these are the thoughts of Bill, not the author. Without resorting to "thought Bill" the writer's grammar tells us something essential to our understanding. But to achieve this effect the author has to remember to backshift all the verbs - not so easy at writing speed.
So while backshifting may be a little-known aspect of grammar, we think it can be helpful once again to make our implicit knowledge explicit. Or, put backshiftingly: We thought this topic deserved an airing. Backshift seemed such an important topic.
Richard Hudson is professor of linguistics at University College, London Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk