  Vocabulary learning by children can be characterized by many biases. When
encountering a new word, children as well as adults, are biased towards
assuming that it means something totally different from the words that they
already know. To the best of our knowledge, the 1st mathematical proof of the
optimality of this bias is presented here. First, it is shown that this bias is
a particular case of the maximization of mutual information between words and
meanings. Second, the optimality is proven within a more general information
theoretic framework where mutual information maximization competes with other
information theoretic principles. The bias is a prediction from modern
information theory. The relationship between information theoretic principles
and the principles of contrast and mutual exclusivity is also shown.
