But who killed him and how?
This work's introductory section "The Problem" states "Spencer is dead. But who killed him and how? This is the problem."  This work goes on to describe the scientific conceptualization of concrete phenomena, which the author terms a "unit act", and expounds on this concept in the chapter "The Unit Act of Action Systems."  This work focuses on relating such topics as psychology, evolution, and economics to its central "Theory of Action".  FTP, identify this sociological work by Talcott Parsons.
This work's introductory section "The Problem" states "Spencer is dead.
The Structure of Social Action