The principles were developed by Koch, the microbiologist who identified the tuberculosis bacillus. At the time they were proposed (late 19th Century), most disease was believed to arise from infectious agents or other, almost completely unknown processes. Koch’s Postulates are still used today to demonstrate causal association between an infectious agent and the development of a disease.

Find a person with the disease, identify the microorganism, culture it, inoculate another animal with the cultured microorganism, and if it develops the same disease as the original person, you have isolated the infectious agent. These principles are in use today over 100 years after Koch proposed them. They work. For infections. For simple uni-causal conditions. However, they do not work for example, to help us identify the cause of lung cancer.

So how do we identify causes of diseases that are not a result of infectious, living organisms that can be cultured in a Petri dish, such as diabetes or lung cancer? For these kinds of diseases a different, but related set of decision tools are needed.