Push Hands: Small Circle, Big Circle

Small Circle push-hands is a rules set which can have moving feet, but really ought to be learned with fixed feet first.  Small circle push-hands allows no grabbing, slapping or striking.  You can only do peng, ji, lu, and an.  The reason it is called small circle is because you are trying to develop peng, ji, lu, and an (ward off, push/poke, draw inward, cover/contain) in a continuous circle, no breaks, no moments of intermittent force.  Small circle push-hands can be completely improvised or it can follow a set sequence.
Once you have established small circle push-hands there are lots of subtler games that can be played from it.

Big Circle push-hands gets it's name because to play it one must break the small circle.  The rule set allows for grabbing (chin na), plucking (zai), elbow strikes, throws, and traps (zhou), forward strikes with the shoulder (kao), and two directional attacks to the opponent's frame which can be light swipes, slaps or sudden jolts(lieh).

Most people learn both big circle and small circle at the same time.  I think that is a mistake, the two rule sets should be clearly differentiated.   The question remains, which is better to learn first?

Small Circle push-hands is the heart of the game, but to deal with an aggressor you must know Big Circle push-hands cold.