RS: The other day, our colleague Julie Taboh told us about a friend of hers, a non-native English speaker. It seems he once tried to tell someone that the person should expect to hear from him again. But instead of saying "I'll get back to you," he said "I'll get back at you." The wrong preposition sent the wrong message. To get back at someone means to take revenge.

AA: Julie had no idea that we had just gotten off the phone with a retired English professor in Canada. David Thatcher has written a book called "Saving Our Prepositions: A Guide for the Perplexed." Actually it's an e-book which you can download free of charge at savingourprepositions.com.

RS: David Thatcher says he thinks the misuse of prepositions is an increasing problem, but it's a problem with a long history.

DAVID THATCHER: "I think it's been pointed out by grammarians for about two hundred years that people don't know how to use them properly."RS: "Well, what are they?"DAVID THATCHER: "They're a part of speech. Let me give you some examples first and perhaps make it easier for you: around, at, before, past, upward, up, in, on. And their job in a sentence is to link or relate one part of a sentence to another. And so you can see them as the connective tissue of language. If you say 'I went the cinema my friend the evening the twenty-fifth,' it resembles a pile of loose bricks."AA: "It sounds like a text message, actually."DAVID THATCHER: "That's right, for brevity. But when the prepositions are added -- 'I went to the cinema with my friend on the evening of the twenty-fifth' -- the bricks are fastened together."RS: "Why have they been such a problem?"DAVID THATCHER: "I think people, perhaps they don't read as much or they are careless about their use. Let me take an example that you've probably heard of. People now say bored of."AA: "Instead of?"DAVID THATCHER: "Instead of bored -- the older prepositions were bored by or bored with. You see, what will happen is that bored of will probably get established. To people of my generation it sounds wrong, it sounds incorrect."RS: "How do you go about learning the correct use of prepositions?"DAVID THATCHER: "I think one way might be to read the good writers, who will rarely make an error of this kind. And a bad way is to listen to interviews with athletes and sports people or even sports commentators. They are very careless about the way they use these terms. And people just simply copy what they hear."AA: "Now for people learning English, prepositions create a sort of a special challenge because of phrasal verbs and the fact that a term, let's say, like to set up, set down, set aside, all mean completely different things."DAVID THATCHER: "That's right. You just have to learn what the speakers use. The phrasal verb might be to fall out with somebody, which means to quarrel or to disagree. 'I would put up with that' means to tolerate. Or to stand up to somebody is to resist somebody and so on. To turn something down is to refuse. All these have to be learned independently without any rules to guide you."AA: "And then there's also context, because these phrasal verbs tend to be more informal, more casual -- "DAVID THATCHER: "Yes, I think so. And I think one should make the distinction between written and spoken English, so that what would be unacceptable in written English would be perfectly allowable in speaking."AA: "In a meeting or in a ... "DAVID THATCHER: "A meeting, that's right, or off the cuff. I mean, many of these mistakes occur -- and perhaps I'm being too strict sometimes because people make these mistakes when they're speaking off the cuff, without preparation and so on. But if they're writing, they should have time to think about what they're putting down on paper and to revise it, or to show it to somebody else for a second opinion, and so on and so forth. So there should be ways of eliminating mistakes of this kind.

"Can I ask you a question? Do you say you congratulate somebody on something, or do you congratulate them for something?"AA: "I say on -- yeah. 'Congratulations on your promotion'? I mean, that sounds ... "RS: "Congratulations for your promotion?"AA: "I'd say on."DAVID THATCHER: "What you will hear a lot is congratulations for. For is one of these cuckoo prepositions that come in and disturb all the other birds in the nest and knock them away."AA: "Wait, so what do you say?"DAVID THATCHER: "I would say that on is the standard way, but there's no doubt that for is elbowing its way in and might replace on in the course of time. So only time will tell whether on will disappear. And that happens many times, that words that were acceptable at one time have ceased to be so."AA:   David Thatcher in British Columbia, Canada, has written "Saving Our Prepositions: A Guide for the Perplexed." It's a free book that can be downloaded at savingourprepositions.com.

RS:   And that's WORDMASTER for this week -- archived at voanews.com/wordmaster. With Avi Arditti, I'm Rosanne Skirble.