Aristotle gives this definition of motion in Physics:
Motion is the fulfilment of what exists potentially, in so far as it exists potentially, namely, of what is alterable qua alterable, of what is movable qua movable,…Motion is in the movable, by the action of that which has the power of causing motion; and the actuality of that which has the power of causing motion is not other than the actuality of the movable, for it must be the fulfilment of both. A thing is capable of causing motion because it can do this, it is a mover because it actually does it. But it is on the movable that it is capable of acting. Hence there is a single actuality of both alike.
If Aristotle had seen Sergei Bondarchuk’s 1966 film adaptation of Tolstoy’s War and Peace, this is how he would have interpreted the dance scene:
Dancing is the fulfilment of what is capable and desirous of dancing. Dance is in the danceable, by the action of one who has the power to lead. The actuality of the leader is none other than the follower, for the fulfilment of both is the dance. Prince Andrei is capable of causing dance because he can initiate it. He is the leader because he actually initiates it by inviting Countess Natasha, who is more than capable of dancing. There is a single actuality of both Andrei and Natasha: their dance.