As observed in Section 1 (pp. 1.4:10-2), actions are caused by entities and not by previous actions. In particular, human actions are caused by human beings, acting as agents of volitional consciousness. Of course, human choices are not made in a vacuum, and (as has been acknowledged several times in this course) their choices will often be affected by external conditions, such as economic, political, or cultural factors. While market conditions do not compel buyers and sellers to act in a particular manner, such conditions clearly exert significant influence on their behavior. Because such influences are not "causes" in a strict sense, but are mediated by volition, they are designated causal influences here.

In this course the causal influences composing feedback loops are represented by arrows. Positive-feedback loops are designated by plus signs, and negative-feedback loops by minus signs. The two concepts will be discussed in further detail in Section 5 and can also be found in the Glossary.