"Preschoolers make a number of assumptions about words and their meaning as they acquire language, one of the most important of which is what the psy… - Malcolm Gladwell

"Preschoolers make a number of assumptions about words and their meaning as they acquire language, one of the most important of which is what the psychologist Ellen Markman calls the principle of mutual exclusivity. Simply put, this means that small children have difficulty believing that any one object can have two different names. The natural assumption of children, Markman argues, is that if an object or person is given a second label, then that label must refer to some secondary property or attribute of that object. You can see how useful this assumption is to a child faced with the extraordinary task of assigning a word to everything in the world. A child who learns the word elephant knows, with absolute certainty, that it is something different from a dog. Each new word makes the child's knowledge of the world more precise. Without mutual exclusivity, by contrast, if a child thought that elephant could simply be another label for dog, then each new word would make the world seem more complicated. Mutual exclusivity also helps the child think clearly. "Suppose," Markman writes, "a child who already knows 'apple' and 'red' hears someone refer to an apple as 'round.' By mutual exclusivity, the child can eliminate the object (apple) and its color (red) as the meaning of 'round' and can try to analyze the object for some other property to label.