Political organization as Europeans understand it was lacking. Among the Semiahmoo there were only autonomous households. These, singly or in small groups, formed recognizable villages, and groups of these villages formed recognizable units that we now call tribes, but neither village nor tribe had any formally separate machinery of government. Kinship, community of interests (resulting from common residence), community of habitual acts, and speech were the basis of recognized units. These were the ties that bound the Semiahmoo People. Weaker ties of the same sort united the peoples of the Straits Salish.
Suttles, Post Contact Culture Among the Lummi Indians
Semiahmoo society was divided into politically and economically independent households. Each plank house held several families united by bonds of kinship. Household heads were usually brothers or male cousins, who took wives from outside the household. The marriages within the community brought a unity by kinship and co-operation, but there was no formal political organization.
In addition to being loosely organized, Semiahmoo society was stratified. It was divided into an upper and lower class of free men and a class of slaves. Slaves were primarily war captives or the descendants of war captives. They were usually treated well but they were given the menial and less pleasant work to do. Free men were identified as high or low people.
High class people were people with "advice", that is, people who knew how to behave properly and who knew their history. Low class people were people without "advise", and therefore they did not know how to behave properly. They were people who had lost their histories.
Suttles, Economic Life of the Coast Salish
Upper class men possessed a knowledge of good manners and of their own heritage. They had inherited privileges which were valued highly. Lower class men lacked this.