Literacy is a really impressive skill; and if you're reading this column, you have it in spades. The sheer quantity of knowledge probably dwarfs any of your other intellectual skills (apart from spoken language).
So at least in this one area, you can almost certainly count yourself as an expert.
However, not surprisingly perhaps, we all have areas of uncertainty.
For instance, take a recent query about the choice between "learned" and "learnt". Are they simply inter-changeable? More precisely, is it the case that we use "learned" in a sentence such as "I have learned a lot today", but "learnt" in "skills are learnt"? In short, that "learned" is the perfect participle, used only after "have", while "learnt" is the passive participle?
What a nice question for grammar gurus full of authority and definitive judgments. The trouble is we're not grammar gurus - we're ordinary language users with no more expertise than you. As we've said before, if you're uncertain, so are we. But we do know how to bring facts to bear on questions like this, and we think some important general morals emerge.
First fact: perfect participles and passive participles are always the same, both in pronunciation and in spelling. It doesn't matter how irregular the forms are - the form you use after "have" (perfect tense) is always the same as the one you use after "be" (passive voice). If you have understood (or mistaken or lost or put) something, it is understood (or mistaken or lost or put). If "learned" was the perfect participle but not the passive participle, it would stick out like a grammatical sore thumb.
We think this is very unlikely.
Second fact: "learned" is more common than "learnt"; but "learnt" is quite common in British writing (though it's rare in American writing). This fact can be found in the Longman Grammar of Spoken English (p397), which is based on 40 million running words, so it's probably right. The same is true of "burned" and "burnt", but with "spoiled" and "spoilt" it's the other way round; and "spelled" and "spelt" are about equally common.
So what? If you're unsure, it's probably because everyone else is, and usage varies. If usage is the ultimate arbiter, as it must surely be, don't expect a clear verdict. So what we all have to learn is to live with uncertainty, and to help pupils to do the same.
Incidentally, what's the past tense of the verb "to text"? Is it regular (texted) or irregular (text) like "put", "set" and other verbs in - t? For an interesting answer, ask a KS3 class; but don't expect absolute certainty.
* Richard Hudson is professor of linguistics at University College London. Geoff Barton is headteacher of King Edward VI School, Bury St Edmunds, Suffolk.