Instead of phase or stage, a period is an interaction sequence in which participants jointly accomplish communicative acts and negotiation functions. The period structure of a negotiation arises from three causes: from efficient cause as parties react to dominate what is happening in the period, from formal cause as the parties enact what they perceive as the proper form of interaction, and from final cause as the parties seek to move from conflict to their goals. The author discusses the four period structures and developments: initiation, dissatisfaction, protection, and termination, with efficient, formal and final causality in the case of Formosa Plastics Group's trying to set the 6the Naphtha Cracker in Ilan 1986-1988.