Skinner, a behavioral psychologist, viewed babies as empty vessels that language had to be put into. Language acquisition, in Skinner's view, was a cognitive behavior of learning by imitation, and believed that operant conditioning affected the child's acquisition of language. Limitations of Skinner's theory are that observations of parent/child language use rarely show parents correcting their child's grammar as would be necessary for operant conditioning; that children may be unable to repeat what their parents say in some circumstances; and that children not fluent by 7 may be unable to catch up.