Falsifiability
Karl Popper had the opinion that only theories that are falsifiable are scientific.<ref>Thornton, Stephen,  "Karl Popper," Stanford Encyclopedia of PhilosophyWinter 2011);  "Science, Pseudo-Science, and Falsifiability,"  1962; retrieved 2012-5-8.</ref> Falsifiability is then a line between science and other kinds of knowledge: if it can be refuted, it is science; it if cannot, then it is not science. Many working scientists think Popper was right.