Have you ever stopped for a moment and tried to identify the different systems that surround you? If you did, you would quickly notice that they are just about everywhere - from your body to your favorite baseball team to the company you work for and the city you live in.

That is because a system is simply a group of element that are connected by relationships that are paired with a purpose. These elements can be physical and visible, but they can also be intangible. For example, while you can both see and touch the branches, leaves, and roots of a tree, things like academic skill in a university are less tangible.

But whether they are physical or not, all the elements of a system are held together by relationships. For example, in the system of a tree, the relationships connecting the various elements are the metabolic processes and chemical reactions. In the system of a university the relationships might be the standards for admission, examinations, and grades.

What then is the purpose of the system?

That is defined by the systems observed behavior, not its stated goals. For example, a government might say that it has a primary goal of protecting the environment, but not put its money where its mouth is. Therefore, environmental protection is not actually the government's purpose as it isn't being reflected by what it actually does.

It is important to know that the purpose and relationships of a system will always define it, even if its elements change. A baseball team might acquire an entirely new set of players, but its relationships between positions and unified purpose of winning games are essentially the same.

Furthermore, the behavior of a system can be broken down into stocks and flows, which change over time.

Here is how they work:

Stocks are the elements of a system that can be accounted for at any given time. For example, water in a bottle, books in a library, or money in a safe. On the other hand, flow is the change in stock over tim as a result of inflows, which add, and outflows, which subtract. Births and Deaths or Purchases and Sales are examples of these.