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(1) phonation—humming with the mouth closed (up to 2 months)
(2) primitive articulation—use of tongue and jaw to form new sounds (1 to 4 months)
(3) expansion—squeals, screeches, whispers, seemingly exploring the range of sounds, pitch, and amplitude—e.g., growls, ‘raspberries’ (3 to 8 months)
(4) babbling—the formation of Baby’s first syllables—da-da-da-da, ma-ma-ma-ma, etc. (5 to 10 months)
(5) sophisticated babbling—the stringing together of various syllables and meaningless sounds which have the rhythm and pacing of real sentences (9 to 18 months)