This paper exams the tacit knowledge involved in building a human tower in Catalonian traditional culture, concentrating on the practice of official members, whose height can get to more than 10 meters. Applying here the perspective of legitimate peripheral participation (LPP) advocated by J. Lave and E. Wenger, we will concentrate on the practice of experienced members or “full participants,” who are little discussed by the authors. A reference point for newcomers, the practice of experienced members will also be important for the community.

From this point of view and based upon our own participant observation in Castellers de Sants, a group of human tower builders in Barcelona, we will find “potential members” who do not participate in daily training but do join in the practice of building human tower at a public plaza. This “no participation” can be understood as a positive attitude: suggesting another possibility as a full participant and constructing a flexible membership to remain an official member. These “potential members” say, “We can come whenever we like.”

We finally point out the importance of “potential members” in the community even though they presently do not participate; they may come to build a higher and more complicated human tower and contribute to its successful result.