Lady Macbeth tries to convince Macbeth to kill the king by attacking his manhood.

If you've read A concise history of the world, you'll have come across this gem. It's an example of a 'misplaced modifier' - that is, a phrase or clause that is meant to belong to one element in a sentence but, because it's been put in the wrong place, seems to belong to another.

Misplaced modifiers are usually obvious and easily fixed: By attacking his manhood, Lady Macbeth tries to convince Macbeth to kill the king; or Lady Macbeth tries, by attacking Macbeth's manhood, to convince him to kill the king.

Sometimes, though, a misplaced modifier is a real impediment to communication. Try this one: Non-alcoholic drinks will be available on the landing that leads from the foyer to the play area for guests' children. Are the drinks for the children, or are we identifying the play area? And what do you make of: Use brand names for the products that are supplied by the manufacturer?

You don't have to be a grammatical genius to stay out of the modifier trap. You just need to think clearly. Ask yourself what the modifying phrase is talking about, and then put it next to that thing. For example, you can fix this sentence by just changing the word order: Abraham Lincoln wrote the Gettysburg address while travelling from Washington to Gettysburg on the back of an envelope.

Often, the cause of the problem is that you're modifying something that's already modified:

Items left in lockers that are unclaimed after six months will be disposed of, where the subject ("items") has two modifiers ("left in lockers" and "unclaimed...") and the second modifier seems to belong to the first. You can often fix this by moving the relative pronoun ("that") and putting in an 'and':

Items that are left in lockers and unclaimed after six months will be disposed of.

Modifiers that apply to the whole sentence should go at the beginning. The manager is sacking the team leader and introducing performance-based pay in an effort to increase efficiency leaves us in doubt about why the team leader was sacked; but In an effort to increase efficiency, the manager is sacking the team leader and introducing performance-based pay does not.