Leung feared that the bigger and stronger Chan would try to claim the Wing Chun lineage after Leung's death.

     Thus, Leung taught him a modified version, less effective version while reserving the pure, traditional form for his sons. Sure enough, after Leung and one of his sons died, Chan drove the remaining son away and assumed Grand-Mastership of the Wing Chun lineage.

     Yip Man eventually became Chan's student. Yip Man learned from Chan for four years before moving to Hong Kong to study at college. There he encountered a kung fu practitioner who revealed his identity as Leung Jan's surviving son, Leung Bik. Leung Bik claimed there had been a divergence in Wing Chun teachings and he then taught Yip Man what he called the traditional Wing Chun system.

     Yip Man would eventually open his own Wing Chun school. As Cheung insists, Yip Man decided to follow the traditions of wing chun, passing on the system to one student only. Yip Man taught the claimed "modified" version to his students and chose to teach the traditional version to Cheung.

Controversy (retrieved from Wikipedia)

     It is claimed that Yip Man's considerable skill increase after training with Leung Bik validates both the existence of the Traditional Wing Chun system and its superiority to the claimed "Modified" Wing Chun. However, Yip Man family Wing Chun practitioners have accused William Cheung of inventing this historical divergence in order to legitimize his own modifications as "secret" elements of Wing Chun. Since the only other possible source of corroboration of Cheung's claims would have been Yip Man himself, it will never be known whether or not Cheung's version of events is true or not.

The Following is a Notation by SiGung Boscola

     Through my years as a Wing Chun practitioner, this historical account by Cheung is the most controversy aspects of the "Traditional" Wing Chun Lineage. Unfortunately, there is no way to validate these claims by Cheung except for the resurrection of Leung Jan, Leung Bik, or Yip Man. Even then, this issue still can be demagogue. Fortunately, I have experience both systems of Wing Chun the so-call "Modified" which is sadly a derogatory term and "Traditional" Wing Chun. Through my experience with both systems of Wing Chun, neither versions of Wing Chun is perfect. For me, the "Traditional" system has a significant advantage over the conventional version of Wing Chun through the use of its expanded theories and footwork. For other practitioners, the conventional system of Wing Chun would be better for them in reference to their body type and preferences. However, politics and financial gain has caused a significant amount of in fighting over this issue and many others. I have been around Wing Chun for many years. I have seen and trained with Chinese and American Masters of both systems of Wing Chun. Politics has always brought the good, the bad, and the ugly of these Masters.

         Any Master to claim to teach the same Wing Chun that was taught by Yim Wing Chun or the original five elders would be absurd. It is the duty of a Wing Chun Master to improve on the system that was taught to them. As long, the system still obeys to the original theories of the Wing Chun system. It is still Wing Chun in every sense of the word. Every Master has always put a bit of themselves in their way of fighting and teachings. This is what makes martial arts an art form in the first place. There is no perfect system, style or way of fighting. As a full contact fighter, I understand that a fight is not pretty. It is an extremely ugly situation. Sadly, movies have portrayed martial combat as something pretty and magical. Real fighting is far from the cinema choreography of KungFu movies.