Howard Jacobson: In the face of overwhelming ignorance, it is the pedant's duty to keep battling on

What the unlettered populace does with words today the rest of us will do tomorrow

Vera Lynn has spoken. "I don't know what Afghanistan's all about," she told The Times this week from her home in Ditchling, Sussex. "I don't know what we are doing there." I'd be surprised if there aren't people in Afghanistan who don't know what Ditchling is all about either. But then I suppose Vera Lynn's point is that Afghanistan has not invaded Ditchling.

It's not my intention to pick a fight with the Forces' Sweetheart. She is 92. If I get to 92 I sure as hell won't know what Afghanistan's about. At 92 I don't expect to know what I'm about. But in a general way I do question the value of ignorance when it comes to expressing a view on world affairs. It is perfectly all right not to know what we are doing in Afghanistan when, say, we are discussing Big Brother. Or vice versa. "I don't know what Big Brother's all about" would be an unexceptionable thing for General Petraeus to tell troops serving in Helmand province. But if you are going to proffer an opinion on the war in Afghanistan then I think you have to know why we are there. This doesn't mean you have to agree with Nato's reasoning. It is perfectly acceptable to say I know what we are doing in Afghanistan and still think we should not be doing it. But to offer your not knowing why we're there as an argument for not being there is absurd. Ignorance is not to be confused with judgement.

Or am I being unnecessarily precise? By saying she doesn't know, does Vera Lynn actually mean that she is unconvinced, that the argument for being in Afghanistan has not persuaded her, that those who should have empowered her with the knowledge to approve the operation have failed to do so?

So hard not to sound punctilious in an age of imprecision. So hard not to sound punctilious when you use the word punctilious.

If I were to tell you that the essayist Sydney Smith defined pedantry as the "ostentatious obtrusion of knowledge" would it make me a pedant? Is pedantry a sort of burr that sticks to you the moment you bring the subject up?

I recall witnessing a furious argument in which one party, sick of being corrected on fine points of grammar, accused the other of being an insufferable pedant. "Ah, yes, pedant," the accused mused, "there's a word with a fascinating etymology." Good joke, I remember thinking. Except that he wasn't making a joke.

If we were to muse upon the etymology of the word pedant together – its first meaning, of course, is schoolmaster – we might wonder why, in general, schoolmasters or schoolmasterly people get such a bad press in our culture. In our best literature, people who know too much are invariably figures of fun, even when they inhabit a world where people know too little. Think of Mary Bennet, the middle sister in Pride and Prejudice, "a young lady of deep reflection" who alone manages to find some redeeming literary quality in Mr Collins' ingratiating letter of introduction – "the idea of the olive branch perhaps is not wholly new, yet I think it well expressed".

She would have made a fine campus novelist, Jane Austen.

Or, where pedants are not satirised, they are written about in such a way as to solicit our compassion not only on their own account but on account of those who mistakenly look to them for love and guidance. That Mr Casaubon has read too deeply and exclusively in the literature of mythology to satisfy Dorothea's yearning is a given in Middlemarch. Scholars don't make good husbands or lovers. They are bound, it is assumed, to bring their pedantry to bed. "In point of fact, my dear, most missionaries eschewed such a position for fear of the chafing of flesh that would surely ensue in a tropical climate. We have much to learn, in this instance at least, from the canine preference, which I am only too willing to essay should you care to signal your compliance."

And if they fare badly in literature they fare still worse in life. We have no regard for schoolteachers. There are countries where to be a schoolteacher is to enjoy considerable esteem. Here, we pay them badly and encourage our children to treat them with contempt. The reason for this is that we fear learning and would rather mock it than acquire it. No one must draw attention to our ignorance, no one must teach us how to think, how to say what we mean or how to mean something better, no one must correct our spelling or our syntax or our speech. The very concept of correction is anathema to us.

The capitulation of the pedant himself to this free-for-all of knowing nothing was in evidence this week on Fry's English Delight, Stephen Fry's Radio 4 programme about the English language. A schoolmasterly man himself, Fry listened, I thought, with regret, as an assortment of language experts – I mean no disrespect: some of my best friends are lexicographers and linguisticians – preached the gospel of wrong is right because whatever the people decide to make of language is what language must become.

Say less when you mean fewer, infer when you mean to imply – none of it matters because what the unlettered populace does with words today the rest of us will meekly do tomorrow. Brute proof, of course, is on the side of those who argue in this fashion; yesterday's sins do indeed become forgotten in the democracy of usage. But that doesn't mean there is not a vice called illiteracy, and that we shouldn't, every now and then, seek to save something from its all-devouring maw.

Take the uninterested/disinterested confusion which Fry's programme mentioned. It is true that these words have changed places over time; that disinterested once meant unconcerned and uninterested meant without bias, whereas it is now the other way around. Or would be the other way around had absence of bias not become a forgotten concept and unconcern – do I look bovvered? – not carried all before it. But it is not pedantry for pedantry's sake that makes one argue for the retention of disinterested. It is because the state of mind it describes – freedom from self-seeking, preparedness to think and act impartially, without taking account of personal advantage, a grand carelessness of profit – is one we cannot afford to lose.

Differentiation matters. Ignorance is not argument. Disinterestedness is not another word for "Whadever!". We are quick to outlaw words when they don't suit the temper of the times. We should, to defy the temper of the times, try rescuing a few.