Abstractness emerges progressively over the second year of life.

words, terms not referring to here and now, are acquired slowly in infancy. They are difficult to acquire as they are more detached from sensory modalities than concrete words. Recent theories propose that, because of their complexity, other people are pivotal for abstract concepts' acquisition and use. Eight children (4 girls) and their mothers were observed longitudinally and extensively from 12 to 24 months of age. Video recordings of mother-infant free play with toys were done every two weeks in a laboratory setting with families in the USA. Children progressively use a range of words referring to abstract concepts, with a major shift from 12 to 15 months and again from 22 to 24 months, but the qualitative data testify an incremental growth of abstract concepts. We identified a progression in the acquisition of words denoting abstract concepts in relation to the overall productive vocabulary, suggesting that having more abstract terms in one's vocabulary promotes faster language acquisition.