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Some time in the second six months of life most children say a first intelligible word. A few months later most children are saying many words and some children go about the house all day long naming things (table, doggie, ball,etc.) and actions (play, see, drop, etc.) and an occasional quality (blue, broke,bad, etc.). At about eighteen months children are likely to begin constructing two-word utterances; such a one, for instance, as Push car.
Brown et al. (Wed,) studied this question.