The Tan sau and Fook sau are two fundamental techniques of the Wing Chun system which are contained in the first set. The Tan sau and Fook sau in the classical version of Wing Chun is practiced in a different way from other versions of Wing Chun which are seen today.
In classical Wing Chun, the Tan sau is always level in the sticking hands when the partners are of equal size. The Fook sau is performed vertically, rather than flat.
The Tan sau is level in order to maximize stickiness. At the elevated position, stickiness is minimized. Once the Tan sau is elevated, it is no longer possible to have a forward pressure towards the opponent's center without slipping.
The flat Fook sau is used by many Wing Chun systems to provide more surface area, and hence, more feeling and detection capability. In classical Wing Chun, the vertical Fook sau is felt to have sufficient detection and control capabilities, while providing a greater variety of counterattack possibilities. One of the key techniques to come out of the vertical Fook sau position is the shocking Chum sau or sinking hand. One of the early generation students of Yip Man, by the name of Lok Yiu, was famous for applying a shocking Chum sau which felt like an earthquake. Just this one technique caused the whole structure of the defender to collapse.
Note: July 1995
In restrospect, the term classical Wing Chun should not be used because who really knows what the real version of Wing Chun as performed by Ng Mui or Yim Wing Chun looked like? The terms classical, original, traditional, etc. are all a bit presumptuous. We don't really know if later versions of the art are better or worse than earlier versions either.