 Up until now, we have been talking about systems on one level of analysis. Our model so far has consisted of simple elements making up systems. The reality of the world we live in, though, is of course vastly more complex than that. And one way of capturing and structuring this complexity is through the use of abstraction and hierarchical structure. Abstraction is the process of successively removing layers of detail from our representation in order to capture the most essential features to a system. An architect's master plan of a building is an example of an abstract representation. It is designed to capture only the most essential features to the building that are required to get an idea of its overall makeup. By using abstraction, we can define different levels to our model depending on its degree of detail or granularity, and this is called encapsulation. We are encapsulating one model of a system inside of another, which in turn may be encapsulated within a third, and so on, creating a hierarchy within our representation. You might ask, what the value of this is? The value of this is that almost all phenomena exhibit this hierarchical structure. Whether we're talking about physical systems where atoms make up molecules which make up substances and so on, or social institutions where individuals make up organizations which make up societies and etc. In order to give some terminology to these different levels, we have at least four different terms we can use. At the most basic level of the hierarchy is what are called elements. Elements are elemental, meaning they do not have constituent components. We treat them as a whole, they simply have properties. An electron is an example of an element. We cannot look inside of it because it is not made up of any separate parts. Next up are subsystems. A subsystem is a set of elements which make up a system which in turn is a component of a larger system. An example of a subsystem may be the brakes in a car. They are made up of elements but are also an integral part of a broader system, the car. Our car, which is a system of personal mobility, is in turn part of a transportation system. And we call this level to our analysis a system of systems. Lastly, all of this is encapsulated within our ultimate unit of analysis, that is the systems environment. Different types of systems base their hierarchy upon different features. So hierarchies within ecosystems are based upon where creatures lie in the food chain. Within social systems, hierarchies may be based upon age, occupation, education, or many other factors. The theory of integrative levels tries to describe the underlying dynamics and characteristics of this ubiquitous feature of organizational levels. The theory of integrative levels deals with the idea that units of matter are organized and integrated into levels of increasing integration and complexity. The idea of integrative levels of organization allows researchers to describe the evolution from the inanimate to the animate and the social world. Higher integrative levels are thought to be more complex and demonstrate more variation and characteristics than lower integrative levels. Because of emergence, each level has its own unique internal dynamics and cannot be fully reduced to the level below. And thus, we have the domains of biology, sociology, and cultural studies because novel features to systems emerge on each of these particular levels of integration that cannot be described by simple reference to physical structures and processes. The last thing to note in this section is that as we have emergence and hierarchical structure, we have a new dynamic between the different levels to the system. As emergence implies that the rules governing any given level may be qualitatively different from those of another, and this will be particularly pronounced when we take the two extremes of the system's micro and macro level. As all of these different levels have to ultimately work together as an entire system, the question turns to whether it is the rules that govern the micro level to the system or the rules that govern the macro level that ultimately determine the system's functioning as a whole. You may also hear this dynamic referred to as bottom-up versus top-down causality and it is another key theme within systems theory. So let's take an example of this. If a doctor has a patient that is in poor physical health and psychologically depressed, does she search for a bottom-up cause to the system's dysfunctionality, in which case she would look for a physiological explanation, something like a virus or infection that is causing the overall problems within the patient's body, or inversely, does she search for a top-down explanation reasoning that it is the patient's psychological state that is inducing their physiological state of poor health? Debating this question further is beyond the scope of this course, but the point to take away is that within these emergent hierarchical systems such as the human body, political regimes, or ecosystems, there will always be this complex dynamic between the rules that govern the system on the micro level and those that govern it on the macro level. We can wrap up then by saying that abstraction is a powerful method of reasoning. By using encapsulation to nest subsystems within systems, we can create models that capture the emergent hierarchical structures that we see all around us in the world.