There is one thing which, throughout the whole of our lives, we never, ever see. That is our own face. The only thing we become familiar with is our mirror image. Yet we know our own face intimately - the curve of the brow, the shape of the nose, the blemish on the cheek.
We recognise ourselves, our friends, celebrities in pictures in the newspapers, in photographs. Maybe a profile might flummox us for a while, but full face hardly ever.
It used to be said that to "Westerners" it was much more difficult to differentiate between the faces of the so-called "pure" races - say the Chinese and the Japanese. This may still be so.
The cartoonist can create a caricature which is instantly recognisable by emphasising just one feature - Tony Blair's "smile", Prince Charles's "ears", Gordon Brown's "bags under his eyes."
I have been reading a piece written by Henri Matisse for a retrospective in Philadelphia in 1947. Included in the exhibition were four line drawings of his face - all very different - yet all obviously Matisse.
The upper part of the face is the same in all four drawings but the lower part varies. In one the jaw is square and massive, in another the chin is elongated, the third - drawn at a slight angle - has a pointed chin and the fourth is totally different from the other three - yet all are obviously Matisse.
He likens this to the leaves on a fig tree, saying there can be quite a difference in the form of the leaves yet each is united by that common quality "fig leaf." The same, he says , applies to all vegetable forms and all fruit - they can have so many different characteristics yet all marrows are obviously marrows, all lemons, lemons.
In the case of his four drawings he says the elements are still always wedded in each drawing with the same feelings:-the way the nose lies on the face, the way the spectacles hang on the nose, the same tension in the gaze. His point is that inexactitude in a representation does not detract from the expression of character or the inherent truth of the personality - in fact these little inexactitudes help to clarify. As he says, "Exactitude is not necessarily truth."
One is reminded of the Graham Sutherland portrait of Winston Churchill which his wife, Clemmie, hated so much that she burned it. Had Sutherland, by inexactitudes, shown aspects of Churchill's character in his face which Clemmie couldn't tolerate?
The portrait at the top is of me at 17.