In the Chinese martial arts society, the title or ranking system follows the traditional family system. Classification of a student's level is not based on his/her skill or actual age. It is decided by who joins the school first. In other words, when you are born into the family. For example, your teacher (male or female) is your father within the system. You should greet him/her as "Si-Fu" (meaning teaching father) to show respect. Your older brother, regardless of age or skill level, would be addressed as "Si-Hing" to show respect. Just as within your own family, there are those whom we address as Uncle, Grandfather, Mother, Aunt, Brother, etc; you address them by these titles to show your respect for them and to show you recognize your place within the family. You may have more than one Si-Fu if you have learned, or are learning, more than one art. In each family lineage you will have one Si-Fu.
In your own family, your father will remain your father for the rest of your life. Even if you go to live with your grandfather or great grandfather, you wouldn't start calling him father. The same is true in the Chinese martial arts title system. Your Si-Fu is forever your Si-Fu in the same family line. Even if you go to your Si-Gung (teaching grandfather) to learn, you must still address him as Si-Gung to show him respect and to show that you recognize your place within the system. An exception is if your Si-Fu is no longer active in the martial world, has passed away, or has left the family for any reason. Then you may call your Si-Gung as Si-Fu. It is perfectly acceptable to learn from different members of the Gung Fu family system, your Si-Gung or Si-Bak for example. But in order to remain respectful and to retain proper lineage, your original place within the system does not change.
The only exception to this rule would be if your Si-Fu kicks you out of his school, cutting you off from the family and you decide to go to a different martial system or to a different lineage of the same system to learn. In effect being reborn into another family. Then you would have a new Si-Fu. But if you leave your original Si-Fu for whatever reason, and go to another school that is within the same family lineage, you still retain your original place within the family. For example, if your father kicks you out of his house and you go to live with your uncle, you wouldn't start calling your uncle, father.
A student should think of himself as a small branch of a tree. The bigger branch that you're connected to is your Si-Fu. The branch above that is your Si-Gung, and so forth, until you reach the trunk of the tree which represents the founder of the system. If you try to remove your small branch from where it is growing and stick it into the tree in a different place, it will stop growing. But if you leave it where it is, it will grow and flourish, and develop small branches of its own.
-Augustine Fong Sifu
TERMS OF THE CHINESE GUNG FU TITLE SYSTEM
SI-JOU An ancestor within the system (deceased)
SI TAI GUNG Your teacher's teacher's teacher, as your great grandfather
SI-GUNG Your teacher's teacher, as your grandfather
SI-BAK Your teacher's Si-Hing, as your uncle
SI-SOOK Your teacher's Si-Dai, as your uncle
SI-FU Your teacher (male or female), as your father
SI-MO Your teacher's wife, as your mother
SI-HING A male classmate who joined the school before you,
as your older brother
SI-JE A female classmate who joined the school before you, as your older sister
SI-DAI A male classmate who joined the school after you, as your younger brother
SI-MUI A female classmate who joined the school after you, as your younger sister