Others in this science-minded group have appropriately mentioned the scientific method. Speaking for my discipline let me sharpen this: When it comes to thinking smart — to sifting reality from wishful thinking — one of the great all-time inventions is the control group. If we want to evaluate medical claims (from bloodletting to new drugs to touch therapy), to assess social programs, or to isolate influences on human behavior we construct a controlled reality. By random assignment we form people into equivalent groups which either receive some experience or not — thereby isolating the factor of interest. The power of the controlled experiment has meant the death of many wild and wacky claims, but also the flourishing of critical thinking and rationality.
professor of psychology at Hope College