"A T'au chooses neither its caste nor its True Name. We are blood born to the first and borne by blood to the second, named for what we have done and might yet do. And like ourselves, our true names are not carved in stone."
- — The Tau'va
The Greater Good, or Tau'va (literally the "Good Greater" in the T'au Lexicon), is the founding religio-philosophical principle of modern T'au society which holds that all sentient beings should strive to ensure the greatest good for the greatest number of beings in the galaxy.
The Tau'va is based on the T'au caste system and is designed to allow for the advancement of the entire T'au society towards a more successful, prosperous and peaceful existence in the future without the violent internecine conflict that marked earlier T'au history.
The Greater Good was first introduced to the T'au during the Mont'au ("Death Age"), the long period of civil war fought between the different T'au cities and clans on their homeworld of T'au before the formation of the unified T'au Empire under the guidance of the Ethereal caste.
It was during this time that the first Ethereals came to the other T'au and united the T'au tribes with the philosophy of the Greater Good. This concept involves the pursuit of perfect societal harmony and combines the particular strengths of each T'au caste to counter the many weaknesses and divisions their culture once possessed.
Within only a few Terran years after the Ethereals first revealed themselves, T'au culture was dominated by the pursuit of the Greater Good and the unified T'au Empire began its long march towards the development of advanced, starfaring technology.
The philosophy of the Greater Good now guides the T'au in their attempts to conquer the rest of the galaxy and unite all the intelligent species in pursuit of the Greater Good. The philosophy forces the T'au to both desire to expand their empire for the Greater Good, and to absorb other intelligent races and their cultures into their own.
However, this expansion could ultimately have disastrous effects upon their ability to actually keep their newborn interstellar empire united.
The ideal of the Greater Good appeals to some of the other intelligent species of the galaxy, and certain units of the Astra Militarum stranded during the Damocles Gulf Crusade and other Imperial conflicts with the T'au are said to have surrendered themselves to the T'au. They now live in the T'au Empire, where such humans are known as the Gue'vesa. Such people are unsurprisingly considered Traitors and Heretics by the Imperium of Man.
During any conflict against other intelligent species, T'au Commanders often urge the enemy leaders to stop resisting the T'au Empire since they will be allowed to retain their own individual faiths and philosophical beliefs as long as they are compatible with the Greater Good.
The Ta'lissera is a sacred undertaking made by the members of a single T'au Fire Warrior team. The ritual bonds the members together in a microcosm of the Greater Good wherein each individual sheds his individual identity in favour of his role in the group.
Those who undertake the Ta'lissera are said to be "bonded," and the ritual is a solemn one indeed in which each T'au spills a portion of their own blood as a sign of their devotion to the whole.
Those who are not bonded view those who are with awe, seeing them as the ultimate adherents of the Greater Good. The ritual of the Ta'lissera is carried out in many areas of T'au society, but is most frequently undertaken amongst Fire Warrior teams, who enter the crucible of war together and often stand or fall by one another's deeds.
The members of a bonded team will go to any length to aid one another, sacrificing their very lives if needed that the team might succeed in its mission. Members of a bonded team often carry ceremonial knifes, while those piloting Battlesuits paint a stylised knife device on their armour.
- Codex: Tau (3rd Edition)
- Codex: Tau Empire (4th Edition)
- Deathwatch - Mark of the Xenos (RPG), pg. 9
- Dawn of War - Dark Crusade (PC Game)