“Single whip (単鞭)” is a technique to let a hand fly like a whip, and smash on the opponent’s face with the open-palm.
It is named because that the left hand is controlled with the right hand just like one long single whip.
This technique is demonstrated 7 times in Chen-style Taijiquan old frame, and 2 times in Simplified 24-form Taijiquan.
A single whip is definitely a typical technique representing Taijiquan.
The usage is that you control the opponent’s left hand with the right hand, and whip your left hand on the opponent’s face.
This is the way demonstrated in the Taijiquan form.
However, the uniqueness of a single whip is rather when it is used for a preemptive strike.
Taijiquan is one of the Chinese northern style martial arts taking a right leading stance normally. It is because it has a traditional skill to let the right fist fly without preliminary action and it can put the weight on the fist when hitting the target.
However, what if the opponent is in a right leading stance, but the left hand suddenly comes out. This left fingertip will fly like a whip from the shade of the right hand. Moreover, even if you retreat back, the fingertip will be extended and chase your face like a whip. Here is the secret of this technique.
In the form, it does not take a right leading stance, but the motion to let the hand fly is same.
It is not shown in the form if it is secret. That is a martial art.
Taijiquan mostly uses counter-attack techniques by inducing the attack from the enemy. The concept of “active attempt to induce an attack” is very similar to the ones in sword techniques of Kage-ryu (陰流) and Shinkage-ryu (新陰流), which are the traditional Japanese martial arts. However, if you can use preemptive strikes as well, “active attempt to induce an attack” will be more effective.