Sixteen- and 24-month-olds' use of mutual exclusivity as a default assumption in second-label learning.

The significance of the mutual exclusivity assumption for early word learning has been questioned on 2 accounts: (a) Children learn second labels for objects, which violates the assumption, and (b) evidence documenting use of mutual comes mostly from older children. This article addresses both concerns. Use of mutual exclusivity predicts not that learning second labels is impossible but that it is harder than learning first labels. To test this, very young children were taught novel labels for objects they either could or could not already name