I know what I like, but I'm not sure about art

Somewhere in the National Gallery I'd like there to be a notice saying, "You don't have to like everything". When you're appointed a trustee, the director, Neil MacGregor, takes you round on an introductory tour. Mine was at 9am, when I find it hard to look the milkman in the eye, let alone a Titian.

We were passing through the North Wing, I remember, and Neil was about to take me into one of the rooms when I said, "Oh, I don't like Dutch pictures", thereby seeming to dismiss Vermeer, De Hooch and indeed Rembrandt. And I saw a look of brief alarm pass over his face as if to say. "Who is this joker we've appointed?"

Of course, I didn't quite mean that. By Dutch paintings I meant Dutch landscape and marine paintings. Feeling foolish about it afterwards I asked myself why I didn't like them and realised it was because as a child I'd been given far too many pictures like them to do as jigsaws. So much sky and so many browns - as landscapes they may be masterpieces but as jigsaws they are a bugger.

There were other casualties of inept or promiscuous reproduction. Gainsborough had a narrow escape due to The Blue Boy, which regularly featured on old biscuit tins, and I believe at one point was a brand of toffee.

And then there was Mrs Siddons, though Gainsborough's portrait of her was confused in my child's mind with the lady in the lunette at the start of Gainsborough Films. This was a British company operating in the Forties and Fifties. The lady posed as if she were a painting then, just before the film began, turned and inclined her head graciously to the cinema audience. Somehow Gainsborough the painter got the blame for this genteel tastefulness.

In those unillustrated days just after the war when so much of English life was on hold my mother would take magazines like My Home or Ideal Home which sometimes included flower prints. Mam would cut these out, put a frame round them out of passe-partout and hang them above the sideboard, thereby so far as I was concerned knocking another school of painting for six.

What is hard to recall about growing up in the Forties and Fifties is that while one did not feel deprived, there was a kind of illustrative famine, a rationing of reproduction, particularly in colour which really only ended in the early Sixties. I don't recall art galleries selling posters, for instance, and the range of postcards was very limited. One of the pleasures of going abroad then - I first went to Italy in 1957 - was to see not merely the pictures in the galleries, but the postcards that were on sale there. They were so glossy and glamorous. This was Art, it seemed to me.

If one can find an explanation like the jigsaws for one's dislikes and blind spots, it's reassuring, makes one feel taste isn't just an arbitrary business. Of course, the greater the artists the more timid one is about voicing one's opinions. I have to say, for instance, that I don't much care for the paintings of Leonardo.

Of course, if he or she is too shamefaced to avow an opinion a writer has a remedy or a resource not available to other people: writers simply put their opinions into the mouths of their characters.

When I did this in 1988 in a play about Anthony Blunt, A Question of Attribution, I can see that this was a flag of distress about art. Blunt tries to explain that the history of art shouldn't be seen as simply a progress towards accurate or naturalistic representation.

"Do we say Giotto isn't a patch on Michelangelo because his figures are less lifelike?"

"Michelangelo?" says Chubb, "I don't think his figures are more lifelike, frankly. The women aren't. They're just like men with tits. And the tits look as if they've been put on with an ice-cream scoop. Has nobody pointed that out?"

"Not in quite those terms."

And I suppose that is what I feel about Michelangelo's women, though don't like to say so. Husky, I suppose, is the word for them - steroidal almost. I don't think she'd be allowed in the 100m dash without giving at least one urine sample.

In A Question of Attribution the Queen is made to have some doubts about paintings of the Annunciation.

"There are quite a lot of them," says the Queen. "When we visited Florence we were taken round the art gallery there and well ... I won't say Annunciations were two a penny but they were certainly quite thick on the ground. And not all of them very convincing. My husband remarked that one of them looked to him like the messenger arriving from Littlewoods Pools. And that the Virgin was protesting that she had put a cross for no publicity."

This last remark, though given to the Duke of Edinburgh, was actually another flag of distress, stemming from my unsuccessful attempts to assimilate and remember an article about the various positions of the Virgin's hand, which are an elaborate semaphore of her feelings, a semaphore instantly understandable to contemporaries but, short of elaborate exposition, lost on us today. It's a pretty out-of-the-way corner of art history but it leads me on to another question and another worry.

Floundering through some unreadable work on art history I've sometimes allowed myself the philistine thought that these elaborate expositions - gestures echoing other gestures, one picture calling up another and all underpinned with classical myth - that surely contemporaries could not have had all this at their fingertips or grasped by instinct what we can only attain by painstaking study and explication, and that this is pictures being given what's been called "over meaning".

I repented, though, when I started to think about my childhood and going to a different kind of pictures, the cinema.

When I was a boy we went to the pictures at least twice a week as most families did then, regardless of the merits of the film. I must have seen Citizen Kane when it came round for the first time, but with no thought that, apart from it being more boring, this was a different order of picture from George Formby, say, or Will Hay. And going to the pictures like this, unthinkingly, taking what was on offer week in week out was, I can see now, a sort of education, and induction into the subtle and complicated and not always conventional moral scheme that prevailed in the world of the cinema then, and which persisted with very little change until the early Sixties.

An audience then had only to see a stock character on the screen to know instinctively what moral luggage he or she was carrying, the past they had, the future they could expect. And this was after - if one includes the silent films - not more than 30 years of going to the pictures. In the 16th century the audience or congregation would have been going to the pictures for 500 years at least, so how much more instinctive and instantaneous would their responses have been? How readily and unthinkingly they would been able to decode their pictures - just as, as a not very precocious child of eight I could decode mine.

And while it's not yet true that the films of the Thirties and Forties would need decoding for a child of the present day, nevertheless that time may come; the period of settled morality and accepted beliefs which produced such films is as much over now as is the set of beliefs and assumptions that produced an allegory as complicated and difficult, for us at any rate, as Bronzino's Allegory of Venus and Cupid.

In his autobiography John Pope-Hennessy talks about discovering paintings in Italy when he was a young man in the Thirties and how "one's impressions of works of art become more vivid in the ratio of the trouble one takes to see them".

Of course he didn't realise how lucky he was. Nowadays everything is trailed and signposted to such an extent that the chances of genuine discovery are very slim; what is hard to find, in Europe at any rate, is something that is hard to find. Still I can see that, when one is occasionally irritated by children scouting round the gallery on some trail or other, what the education department is trying to do for them, even artificially, is give them some sense of discovery about paintings.

Seeing them sitting round their teachers on the floor of the gallery I wonder whether they'll ask the questions that really puzzle them. It always used to bother me as a child, for instance, that the crucifixion of Christ was always depicted as more decorous than that of the thieves, their agonies much more graphic and protracted that his, who ought to be their superior in suffering as he was in everything else.

Jesus's crucifixion was also much more attended to. And I wondered why one of the Holy Family couldn't occasionally walk over and pay one of the other crosses a visit. The thieves after all never had any family with them, and it's what we always did if we went to see someone in hospital and there was someone on the ward with no visitors.

It must be harder though for many children coming into the National Gallery now than it was say 30 years ago, simply because their knowledge of Christianity is much patchier than it was then, not to mention of course their knowledge of classical myths.

Still almost any reaction in front of a picture is better than none. The portrait of Alexander Mornauer only came into the collection in 1991 but had it been here 20 years ago a child might have been struck by its resemblance to the TV actor Raymond Burr portraying the detective Perry Mason. And that, of course, is not the kind of remark that would have gone down well with Sir John Pope-Hennessy, but it doesn't matter. You've got to start somewhere and anything that hooks you on to a picture and makes you look again at it is better than nothing. And certainly more helpful than being told, "You should look at this. It's a masterpiece".

You are reading a book - a novel, say - you come across a thought or a feeling which you've had yourself and thinking it peculiar to yourself, you haven't expressed it or communicated it, and now here it is set down by someone else. And it's as if a hand has come out and taken yours.

Something similar, which one might call evidence of humanity, happens in pictures. The most notable example in one of the most popular paintings in the gallery is in the Piero Baptism ... and it's the man taking off his shirt. There's something obscurely comforting in the fact that they took their shirts off 500 years ago much as we do now, this piece of naturalism more vivid for its contrast with the hieratic figure of Christ and the Baptist in the foreground who are, of course, like all the figures in Piero's pictures, stern and unsmiling. They wouldn't get far advertising toothpaste, Piero's people.

This is an edited version of a lecture, 'My National Gallery', that Alan Bennett will deliver at the National Gallery, London, tonight.