How many words do dogs understand?

"I'll teach my dog 100 words," says the boy in the children's story of the same name। But can he really? Dog owners love to gush about canine intelligence. So it would come as no surprise to them that research supports their beliefs that dogs have a profound mental capacity. But how much of our language do dogs really understand? It turns out that the language comprehension of some dogs rivals that of and parrots, not to mention the average 3-year-old।

Sure, most dogs understand the basics --"fetch," "sit" and "stay." But if you have the motivation and patience, you will probably be able to teach your dog even more than 100 words. Stanley Coren, a psychologist who has performed a significant amount of research on the subject of dog intelligence, suggests that average trained dogs know about 160 words [source: Coren]. Some dogs even show a vocabulary as vast as a human toddler's.

Since at least the 1970s, when researchers successfully trained chimpanzees to use and read words in sign language, we have known that language, in a loose sense of the term, is not unique to humans. Animals have the brain power to understand human language and use their own languages in surprisingly profound ways. We all know parrots can be trained to speak human words. And dogs will react to the word "walk" with a knowing, tail-wagging enthusiasm.

How deep is the dog's bank of human words? On the next page, we'll take a look at one border collie's remarkable talent at retrieving objects of different names.