Definition: The theory doesn't explain anything other than the phenomenon it explains.
- There was hostility toward hippies in the 1960s because of their parents' resentment toward children.
(This theory is flawed because it explains hostility toward hippes, and nothing else. A better theory would be to say there was hostility toward hippies because hippies are different, and people fear things which are different. This theory would explain not only hostility toward hippies, but also other forms of hostility.)
- People get schizophrenia because different parts of their brains split apart.
(Again, this theory explains schizophrenia - and nothing else.)
Proof: Identify the theory and the phenomenon it explains. Show that the theory does not explain anything else. Argue that theories which explain only one phenomenon are likely to be incomplete, at best.