Many theorists have included various types of collective phenomena and behaviors in the concept of “collective behavior”, and each theorist has given his/her own definition to collective behavior. This plethora of definitions hinders research progress and there is a need of a more exacting operalization. This paper reviews many of the tautology and ambiguous meanings of “collectivity” in explanations for sequences of formation of collective behavior in such works emerging from, among others, the Chicago school: from R.E.Park and H.Blumer to R.H.Turner =L.M.Killian. As an option to the above, the gathering/assembling proces model, which focuses on how individuals' actions become collective, would contribute the resolution of these conceptual problems.