Each pueblo is a tribal unit formed of few or many clans, as the case may be, always matrilinear in descent. Each is wholly independent of every other and all have had a republican form of government from the earliest times. Under very great stress of emergency, tribes have been known to combine for a brief period, but ordinarily they crossed one another’s path in peaceful times only for purposes of trade, or as Bandelier puts it, “It may be said that no two tribes were ever so hostile as never to trade, or so intimate as never to fight each other.” The designation of titles and of official duties in these self-governing villages varies more or less from tribe to tribe, but in essentials the recent investigations of scholars incline them to believe in a fundamental similarity. There has been much discussion as to the priority of clan or of kinship in the up-building of the economic fabric of pueblo society. The position of Kroeber seems the most simple and natural. He contends that clan functions are too vague and remote to allow them precedence over the normal and inherent relations of every created being. Quoting him: “To blood ties they are blindly loyal and instinctively affectionate. Outside all are but associates.” If further intercourse cements esteem, any one, of whatever race, “even a Navajo,” may be held more dear and less hostile than one of their own tribe. Again Kroeber says, What is clear is, that there is in the Pueblo mind and has been for centuries past, a concept of a definite and characteristic scheme of clan organization which belongs to no one nation but is common to all. The whole nature of the existing clans in the Southwest is that of an organ in a body.[143] One remarkable and characteristic feature that prevails in the clan system is the grouping of clans in pairs. It is very prominent in Hopi, and though not directly established for Keresan Pueblos, it appears probable because the same pairs frequently occur in that nation. Kroeber differentiates the family and clan as follows. The clan is a ceremonial institution, whereas the family is the foundation of society and is centred in the house as a basic concept. The house belongs to the women of the family, not merely as they are living to-day, but from the long past in successive generations. “There they have come into the world, pass their lives, and within its walls they die.” True, the clan is maternal and totemically named, and also the same terms of relationship are applied to its members as to those of blood kindred. While this is an undoubted source of confusion to strangers and to the student of its culture, there never is the slightest ambiguity in the native mind between the two.