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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 apes 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.

After being featured on a television show for his ability to understand 200 words, a border collie named Rico intrigued some researchers at the Max Planck institute. These researchers asked if they could bring Rico in to perform some experiments to find out just how far they could stretch the dog's language ability. The answer: surprisingly far.

At first, the researchers wanted to verify in a controlled setting whether Rico really knew 200 words. To do this, they collected 10 items with which Rico was familiar. At the verbal command of his owner, they had him fetch a specific item from a separate room. Rico performed very well at this task, but the researchers wanted to challenge him further. Next, they chose a new item — one that Rico had never seen in his life — and placed it in the room among the familiar items. The owner requested that new item by name and, lo and behold, Rico brought back the new item.

Researchers performed this test several times, each time with another new item, and found that Rico brought back the correct item an impressive 70 percent of the time. This demonstrated not only that the dog had a large vocabulary, but also that he knew how to use process of elimination.

Impressed as they were, researchers pushed Rico further with an even more difficult task. They wanted to find out whether Rico could remember the items that he learned in the experiment after only one exposure, a process called fast-mapping, which children can do. One month after Rico proved his language abilities in the lab, researchers brought him back in. This time, they put one of the new items that Rico correctly fetched a month earlier in a room with four familiar and four unfamiliar items. When his owner requested it, Rico was able to correctly fetch the item he had learned a month previous as much as 50 percent of the time. Though that might not seem remarkable, it was to the researchers, because this success rate compares with that of 3-year-old children.

However, whether a dog's "understanding" of a word compares to a child's is another matter.

When kids learn language, they start by associating sounds with objects or ideas. For instance, if a child hears the word "bottle" every time the child is presented with a bottle, the child will eventually learn to connect the sound of the word with the object. In this way, kids understand words before they learn to express them. One could say the same thing happens with dogs. Dogs just never make the next step to speak with words. However, whether a dog's "understanding" of a word compares to a child's understanding is another matter.

When a toddler learns a word, such as "pencil," the child will associate the word with the concept of a writing instrument in a variety of ways (even making the mistake of calling a pen a "pencil" after seeing someone write with it). On the other hand, dogs probably learn the word "pen" as a sound that commands a response — "bring me the pen and you'll get a treat," for example.

Because dogs most likely don't understand abstract concepts, they can't understand the words that refer to abstract concepts. For example, humans understand ideas like "love," "hatred," "beliefs" and "carelessness." These ideas don't necessarily relate to a specific object or action. Ideas that do refer to specific things are called concrete concepts. So, when we tell dogs we love them, this probably doesn't mean as much to them as the word "treat" does. Some might say that until we find a way to interpret a dog's mind, we can't definitively say that dogs don't understand abstract concepts. As far we know right now, however, dogs are only capable of understanding words that refer to concrete things.

Can we say that a dog understands language? That depends on the definition of language, which is contested. If language indicates the process of merely communicating a particular stimulus (a word) to produce a particular reaction, then dogs definitely understand language. But for many linguists, people who study language, a proper definition of language must go deeper.

Some linguists think language necessitates sentences with syntax. Syntax refers to the way words relate to each other in a sentence, based on a structured rule system, such as word order. For instance, for English speakers, the sentence "the dog bites the man" means something different from "the man bites the dog," even though both sentences incorporate the same words. Under the umbrella of this stricter definition of language, dogs don't understand language because there's reason to believe they can't understand sentences in this way. Even toddlers can distinguish between parts of speech such as verbs and nouns, while a dog probably can't [source: Kaminski]. One might argue that if dogs can't use syntax like children can, then dogs can't truly understand a word because they don't understand how it relates to other words.

But if dogs can't really comprehend language in the way humans do, why do they seem to understand us so deeply? Certain studies show that dogs pick up on human gestures and cues (like Clever Hans did) better than other animals, even great apes [source: Hare]. So when dogs seem to understand our words, they might really just be reading our body language or tone of voice.

Regardless, dogs have an amazing ability to understand us.