When learning any movement practice, whether it is dancing or martial arts, it is much more efficient if we understand the basic principles of movement. Our posture and movement are controlled by specific controlling mechanisms of our sensory-motor system. This basic fact was first discovered by the Australian Frederick Matthias Alexander, the creator of the Alexander Technique, which subsequently led to the field of somatics. Alexander made the discovery that our posture and movement are controlled by switches in the body, what he calls primary controls.
To understand this we can look at what happens when we execute a simple action of picking up an object such as an apple. The action is initiated by our eyes scanning and recognising the object and our head then reorienting to face the object. The turning of the head creates tension in the neck which then leads the body to reduce that tension by readjusting and orienting towards the object and then to approach it. We reach for the object and grasp it with our hand. The body braces itself anticipating the weight of the object which is sometimes evidenced by the fact that if the object is much lighter than expected the hand will fly up and we are startled.
The body follows the extremities: (1) the gaze and head; (2) the arms and legs. In other words, the body follows and adjusts to movement that is initiated from these extremities. While we normally use our legs/feet to connect to the ground and walk, we can use them in a similar manner to arms/hands to reach and manipulate things, eg., to move objects and the body will reorganise to allow that to happen.
This insight is extremely useful in understanding how we can initiate movement in a situation like social tango. While show dancers can be seen to look around and move their arms to direct their movement, in a close embrace social tango we are in a tight and unchanging embrace. This means that our eyes and hands are not available to initiate and control movement. All the movement is below the waist, in the legs and feet. It means that we must use our legs and feet as our eyes with which we scan around and as the primary controls that initiate movement in a given direction.