Stage II (1-4 months): First Acquired Adaptations
-Primary Circular Reactions
-Imitation: "Vocal Contagion"; mutual imitation of familiar activity if initiated by infant.
Stage III (4-8 months): Procedures to Make Interesting Sights Last
-Secondary Circular Reactions
-Imitation of familiar visible actions
Stage IV (8-12 months): Coordination of Secondary Schemes
-Concatenation of secondary circular reactions
-Imitation of novel visible and familiar invisible events
Stage V (12-18 months): Active Experimentation
-Tertiary Circular Reactions
-Imitation of novel invisible events (by trial and error)
Stage VI (18-24 months): Mental Representation.
-New solutions without overt trial and error
-Language
-Pretend and symbolic play
-Deferred imitation