The rule is: the word 'it's' (with apostrophe) stands for 'it is' or 'it has'. If the word does not stand for 'it is' or 'it has' then what you require is 'its'. This is extremely easy to grasp. Getting your itses mixed up is the greatest solecism in the world of punctuation. No matter that you have a PhD and have read all of Henry James twice. If you still persist in writing, 'Good food at it's best', you deserve to be struck by lightning, hacked up on the spot and buried in an unmarked grave.

Sticklers never read a book without a pencil at hand, to correct the typographical errors. In short, we are unattractive know-all obsessives who get things out of proportion and are in continual peril of being disowned by our exasperated families.

We read privately, mentally listening to the author's voice and translating the writer's thoughts. The book remains static and fixed; the reader journeys through it.

The problem is that it has become politically awkward to draw attention to absolutes of bad and good. In place of manners, we now have doctrines of political correctness, against which one offends at one's peril: by means of a considerable circular logic, such offences mark you as reactionary and therefore a bad person. Therefore if you say people are bad, you are bad.

It used to be just CIA agents with ear-pieces who walked round with preoccupied, faraway expressions, and consequently regarded all the little people as irrelevant scum. Now, understandably, it's nearly everybody.

Truly good manners are invisible: they ease the way for others, without drawing attention to themselves. It is no accident that the word "punctilious" ("attentive to formality or etiquette") comes from the same original root as punctuation.

Punctuation marks are the traffic signals of language: they tell us to slow down, notice this, take a detour, and stop.