How to solve crosswords

Last week we saw the golden rule for deconstructing a cryptic crossword clue: when approaching one, leave behind all grammatical, philosophical and other preconceptions. The spotlight this week is on the apostrophe.

In a clue, an apostrophe can be performing any of three functions. The one leading to the solution is almost certainly not the one that the surface meaning of the clue would immediately suggest to a normal reader.

The apostrophe could be there in its possessive form (Jane's = belonging to Jane); or as a contraction for "is" (Jane's = Jane is); or as a contraction for "has" (Jane's = Jane has). So, for example, "the king's evil" in a clue could indicate a) an evil associated with the king (for example scrofula, which the monarch's touch was supposed to cure); or b) the king is evil; or c) the king has evil.

To show how this works, here is a clue from last week by Audreus: "River's direction can be deceptive (5)". The surface meaning is intended to get you thinking about the direction of some river wandering all over the place. On the face of it, "deceptive" might be an anagram indicator, but the only five letters in the clue that could be the anagram fodder are CAN BE, and no word made up of these five letters comes to mind.

So try for size "River is direction" or "River has direction". Bingo! The Fal river in Cornwall is a waterway much beloved of setters. (Another, for some reason, is the Po, in Italy.) And southeast (or SE) is a direction. If FAL had SE, deceptive would therefore be FALSE.

And here is another clue by Paul, also from last week: "Antelope's short dash (4)". Put out of your mind all thoughts of an antelope making a short dash. In this case, it's the antelope that's short, not the dash. If an ELAND is an antelope and if it were short, you would end up with ELAN, which is that combination of style and vigour that we also know as dash.

Falling into a similar category to the apostrophe is the group made up of the words "a", "an", "one", the capital letter "I" and the figure 1. To setters, they are all interchangeable. They can write any of them to indicate that one of the others is somewhere in the solution. Even more sneakily, they can write "one's" ("one has S") to indicate IS, or "first" (ie 1st) to indicate IST.

Finally, here is an example of Enigmatist up to this trick: "A cosmetic joke (3-5)", where A = 1 and the cosmetic is an (eye)liner, giving you a ONE-LINER.

· Hugh Stephenson's book Secrets of the Setters: How to Solve the Guardian Crossword is published by Guardian Books, price £12.99. You can order it on 0870 836 0794, online at bookshop , or from bookshops.