Frankly, I never saw the idea that a theory has to be "Falsifiable" emphasized as "essential" until I saw it used as an argument that intelligent design can't be a theory. The understanding of the scientific method I grew up with did not include that as a necessary condition. Instead, the basic steps of the scientific method as I understood them are pretty much summed up by the author of the notes at http://teacher.pas.rochester.edu/phy_labs/appendixe/appendixe.html#Heading6: "1. Observation and description of a phenomenon or group of phenomena. 2. Formulation of an hypothesis to explain the phenomena. In physics, the hypothesis often takes the form of a causal mechanism or a mathematical relation. 3. Use of the hypothesis to predict the existence of other phenomena, or to predict quantitatively the results of new observations. 4. Performance of experimental tests of the predictions by several independent experimenters and properly performed experiments." Ever since the idea of "falsifiability" as a necessary aspect of a theory came up in association with the "intelligent design" thing I've been skeptical. In my opinion, for example, the germ theory of disease is not falsifiable. Even if we were to infect a population with certain "germs" and no illnesses resulted, that would not falisfy the theory because other factors could be involved. Instead, the germ theory of disease is based on positive demonstration. Falsification has been involved, but it's been falsification of null hypotheses in order to infer acceptance of the alternative hypothesis that "germs" cause disease. Anyway, today I got around to just doing a Google Search on "Does a theory have to be falsifiable." What I found is that it's not an element of the scientific method. It is a philosophy proposed by Karl Popper and it is not universially accepted. Here's an example of what I found: Falsifiability: Definition from Answers.com Here's another interesting article: Association for Asia Research- Defining science A key quote: "Many modern scientists believe that falsifiability is a necessary feature of a scientific theory. However, Thomas Kuhn, who is the author of The Structure of Scientific Revolutions, disagreed with Popper. According to Kuhn, scientists tend to be dogmatic in seeking confirmation of established paradigm even in the light of conflicting data. Scientists stubbornly try to fit observed anomalies into their paradigm. Scientific revolutions have occurred in history, but only rarely, when an entire paradigm is in crises. In short, according Kuhn, falsifiability cannot be a criterion of science because it excludes the larger aspect of what scientists actually do." I think you can pretty clearly see from that discussion that Popper's philosophy is not a "rule" of the scientific method. I should have known. Once confident, dogmatic, and false statements were made. Don't get me wrong, I don't see how "intelligent design" could be inferred as the cause of what we see through the scientific method. But this thing about "it can't be a theory because it's not falsifiable" as though that an established rule of the scientific method is a crock.