本书所进行的研究始于一个简单的问题：为什么现有的国际关系理论无法预测冷战的终结和“9·11”事件等国际性、结构性变化？由于现有理论缺乏对系统变化的解释，尤其缺乏对系统演化机制的具体内容的解释，因此笔者借鉴自然科学中复杂性理论能够弥补一些既有理论的不足。

首先，主流理论基本上是体系层面理论，是宏观结构理论，属于一种自上而下线性分析模式，其分析焦点停留在系统稳定和系统均衡。现实中我们往往将理论的简约性等同于科学性，因为变量最少的模型才能够为变量之间的因果关系提供一个明确的逻辑。但是，如此多变复杂的国际政治仅用少数的变量来分析，势必只能得出有限的结果。理论再简约，但如果不能反映现实，那么理论的价值和务实性便将大打折扣。按照复杂性理论的逻辑，世界政治的复杂性来源于变量之间的非线性互动，说明了复杂性不仅是变量数目的问题。通过概括经验事实与分析观察到的数据，实证主义认识论根据事件发展的前后顺序，寻找以最大的确定性与最严格的“必然性”为基础的因果关系，但未对“偶然性”变量与微观层面的变量之间自下而上的复杂互动产生的系统效应，给予充分的关注。

其次，复杂性理论研究复杂系统及其结构和行为，与现有系统理论具有相同的基本构成要素，即结构和互动的单元，但除此之外，复杂系统还包含外部环境因素。外部环境因素包括技术、物理、经济、地理等与社会政治系统既相互区别又密不可分的系统。比如，地缘政治与地缘经济等概念告诉我们，自然地理与政治、社会和经济存在无法分割的互动关系。事实上这是把国际体系看作一个有机体，或者说“活的系统”或者说开放系统，而不是一个封闭系统。开放系统不仅包含维持动态平衡所需要的负反馈，还包括引起系统演化的正反馈。这意味着我们不能把“其余条件同等化”，只关注一个变量的变化结果，而是需要关注变量之间的集体相互作用衍生出来的宏观结果。复杂性理论分别把它称为“涌现”和“协同进化”。

最后，既有理论习惯使用微观经济学方法，比如还原论、博弈论或者定量分析等理性主义和个体主义方法论来研究宏观结果与国际事件。但是，仅从常识上说，通过分析国家的理性选择或决策者的预期效用去分析系统层次的宏观事件（比如战争），需要超越多少个分析层次呢？可能这因果关系的中间还存在无数个分析层次，比如官僚机制、社会、国家、超国家、地区等。事实上，我们不可能通过分析某一个人体细胞或器官的属性去理解一个人的行为，而是应该研究各个细胞与器官如何交互进而引导人的行动。同样地，分析系统层次的国际后果时，研究起点应该放在微观层面变量交互及其对上位层次衍生出的宏观结构，及其变化机制。此外，如批判理论指出的那样，主流理论，尤其是理性主义理论只在给定的、先验的结构内有效，是一种问题解决理论，系统变化本身不是它们的研究兴趣点。复杂性理论则不同，它为系统演化从内部研究机制方面提供了一个具体的解释。

复杂性理论认为，行为体的理性是有限的，但与社会进化理论不同，复杂性理论认为行为体是有目的性、战略性的主体，而非被动的、进化的个体。通过学习、探索、反思和适应等能动性活动，可以弥补其有限理性的不足之处。在微观层面单元之间的这种集体互动又会与外部环境相互作用，并推动宏观层面的演化。复杂性理论将这一进程称为“自组织”。如果变化累积到一定的临界点，一种突变（而不是渐变）现象会发生，其结果就是系统变化。复杂性理论的各种方法论，比如基于个体建模、计算机仿真和反事实推理等就是出于追踪这种动态的微观—宏观变化的目的。这一逻辑也等同于科学实在论所提倡的认识论，即认为解释应该是生成的，而不是从不变规律中发掘而来的。

现有文献大多将国际关系理论的方法论和科学哲学方面出现的复杂性转向作为研究重点，但对具体领域的案例研究还有待进一步展开。这在一定程度上说明复杂性理论难以操作的一面。复杂性理论涵盖了许多相互联系的学科，比如混沌理论和进化理论、涌现理论等，因此各个学者对复杂性理论的理解存在明显差异。与学者们致力于完善建构主义，或推动实践转向，以进一步发展国际关系的社会性因素形成鲜明对比的是，无人尝试完善和整合以复杂性为基础的国际关系理论。本书的目的是构建一个初步的复杂性国际关系理论，以期能对现有理论体系有所贡献。为此，本书采用了理性主义理论在三个不同层次的三个核心假设，即无政府状态、国家中心说和国家理性说，并以此对现有理论体系进行一个复杂性修正。复杂性理论认为：第一，系统层面上的组织排序并非无政府状态，而是有组织复杂性，这意味着国际体系的本质是一个有序和无序混合的状态。第二，单位层次上的分析焦点在于变量互动，即单位之间、单位和外部环境之间的协同进化如何产生宏观层面的变化，这是一种自下而上、自上而下相结合的分析模式。其三，个人层次，国际行为体不仅有国家，还存在其他行为体，而且它们都是有限理性的。

本文具体谈这一修正的三个分析层次及其对推动国际变化的作用。每一个分析层次分别对系统演化提供了一种演化机制的解释。最后，本文将再次论及现有国际关系理论体系的缺陷，重申复杂性科学的理论内涵、实践要求与国际关系理论进行复杂性转向的必要，探讨如何选择适用于复杂性理论的案例，提出了还需进一步研究的相关问题。

关键词：复杂性理论 复杂系统 国际关系理论

Abstract

Why were mainstream IR theories unable to predict international and structural changes such as the end of Cold War and“9.11?”Existing theories lack explanation regarding systemic change,especially with regards to explanation on specific mechanisms of change.Thus,complexity theory can play a supplementary role to existing mainstream IR theories.

First,mainstream theories are system-level theories,and also macrostructural theories.They are in nature top-down,linear analytic models,confined to analyzing systemic stability and international continuity.In the field of natural science,this kind of analysis is called Newtonian determinism.We tend to believe that a theory's parsimony equals to scienticity,because it guides a very clear logic of causal relationship between variables.Yet,in today's complex international environment,using only a small number of variables and limited information is not likely to have much predictive ability.Theory however parsimonious,if it cannot reflect reality,then its value and practicality is likely to be questioned.According to complexity theory,the complexity of world politics comes not only from increase in the number of variables in question,but also from the non-linear interaction between these variables and the unintended macro-level systemic effects they produce.Positivist epistemology and state-centric IR theories built upon it search for nomological causal relationship from observable events,while constructivism focus on the systemic structure's constitutive role,but both rationalist and constructivist theories look the other way when it comes to dealing with contingent variables,plural non-state actors，or bottom-up,complex interaction between variables and processes on the micro-level.

Second,complexity theory analyses and studies complex systems and its structure and behavior.Systems share the same components such as structure and interacting units as other IR systems theories.But complexity theory further adds the“external environment”as a system component.External environment includes technology,weapons,physical,economic and such systems differentiated from,but deeply inter-connected with,and can exert a great amount of influence on the international political and social system.In effect,this is looking at the international system as a“living organic system”,and not a closed system.An open system would include not only negative feedbacks that mainstream theories assume for a homeostatic systems analysis,but also positive ones that would induce systemic change.This means that we cannot“hold all other variables constant,”while tracing the change that only one variable occurs.Rather,we should look at the collective interaction between variables on the micro-level and the macro-results they produce.Complexity theory defines this as“co-evolution”and“emergence,”respectively.

Third,exiting mainstream theories use classical micro-economics as its main methodology,for example reductionism,rational choice,game theory,quantitative analysis,all which are essentially individualistic under the rubric of rationalist tradition,to predict macro-results and international events.Yet,analyzing a nation's strategic choice or a leader's expected utility to predict macroresults and systems-level phenomena,such as war,will have to transcend countless levels-of-analysis.Perhaps in-between this causal relationship might exist the bureaucracy,society,state,transnational state,regions,and etc.Furthermore,as critical theories would argue,rationalist theories are valid only within fixed,given structures,in essence they are problem-solving theories.Systemic change has never been their focus of interest.In this respect,complexity theory can make a theoretical contribution because it provides a concrete explanation regarding systemic change and the internal mechanism of change.

Complexity theory assumes that actors have bounded rationality,but unlike social evolutionary theory,actors are intentional,teleological and strategic organisms.Individual and social agency implies that actors can make pro-active choices such as learning,searching and adaptation,through which actors can supplement its bounded rationality.Such collective unit-interactions on the micro-level will also interact with the external environment,ultimately leading to“co-evolution”on both the micro-macro levels of the international system.Complexity theory refers to this process“self-organization”.When change within the system is accumulated and reaches a critical point,then abrupt（and not gradual）change will occur,what IR refers to as systemic change.Various methodologies of complexity theory such as agent-based modelling,computer simulation,and counterfactual thinking,is used to trace such micro-macro dynamic change.This logic also equates to the epistemology of scientific realism,which argues that explanation should be“generated”and not simply derived from unchanging laws.

Therefore,this book strives to establish an IR theory based on complexity.To do this,I use the three main assumptions of rationalist IR theories built on three different levels-of-analysis,i.e.anarchy,state-centrism,and actor-rationality,and offer a complexity-turn perspective.First,complexity theory argues that on the systems-level,the organizing principle is not an anarchic absence of higher authority,but rather“organized complexity”,meaning a conflation of order and disorder.Second,on the unit-level,the analytic focus is on variable-interactions,tracing the co-evolution of inter-unit interactions and unit-environment interactions and how they produce change on the macro-level.In essence,this is a bottom-up and top-down combined analytical model.Doing so will supplement the shortcomings of reductionism and holism,and also the long social science debate regarding agent and structure.Third,on the sub-unit level,international actors are not only confined to states but also non-states play an important role on global stage.All actors have bounded rationality.The main part of the dissertation deals with each of the three complexity-based levels-of-a nalysis in detail,i.e.analyzing the shortcomings of mainstream IR assumptions in explaining systemic change and why and how complexity theory's assumptions can supplement them.Each level-of-analysis provides explanation on the mechanism of systemic change.In conclusion,my dissertation talks about the need for a complexity-turn in IR theory and its scientific philosophy,as well as further area of study required in the future.

Keywords: Complexity Theory,Complex System,International Relations Theory

This paper adopts three core assumptions of the theory of rationalism at three different levels, namely anarchy, theory of the national center and the theory of national rationality, and makes a correction regarding complexity to the existing theoretical system. This paper discusses the three analytical levels of this amendment and its role in promoting international change. Each level of analysis provides an explanation for the mechanism of evolution of the system. Finally, this paper discusses the defects of the existing theoretical system of international relations, restates the theoretical connotation and practical requirements of complexity science and the necessity of complexity changing of international relations, and discusses how to choose a recommendation, which is suitable for the theory of complexity, and the related problems that need to be studied further.