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1) reflexes (0-1 month) that gradually become more efficient: sucking, grasping, kicking.2) primary circular reactions (1-4 months) repetition for own sake without any intention.3) secondary circular reactions (4-6 months) repeated actions to produce effects that seem interesting.4) coordination of secondary reactions (7-10 months) mastery of responses that child uses to create specific desired effects.5) tertiary circular reactions (11-18 months) active trial and error experimentation.6) internal mental inventions (18 months) invention of new means of affecting self and world through internal mental combinations.