The title refers to the work's construction in 174 units, mainly composed in what Stockhausen terms "groups"—cohesive groupings of notes unified through one or more common characteristics (dynamics, instrumental color, register, etc.): ""a particular number of notes which are joined, by means of related proportions, into a superordinate experiential quality" (namely, the group). The various groups in a composition have various proportional features—various structures—but they are interrelated in that the properties of one group may only be understood by comparing them in degree of relationship with the other groups". This category is contrasted with the "punctual" style of early Darmstadt serialism, which nevertheless also occurs in "Gruppen", along with a third category of "collective" or "statistical" swarms or crowds, too dense for the listener to be able to accurately distinguish individual notes or their order of succession. Consequently, the importance of individual notes is relatively low, so that sonority, density, speed, dynamics, and direction of movement become the main features for the listener.