The Story of Clever Hans - The Law of Parsimony
Not all explanations for a knowledge claim are created equal. Some explanations involve more details and make more assumptions than others. Assume you are confronted by two explanations for the same phenomenon. Both explanations seem equally plausible. Which one would you select: the one that involved numerous assumptions and details or the one that involved fewer assumptions and details? If common sense tells you to select the explanation that makes the fewest assumptions (remember assumptions also require explanations), then you already have a good understanding of the Law of Parsimony.
Here's an old but excellent example of the Law of Parsimony. In the early 1900s Mr. Wilhelm von Osteen, a retired mathematics teacher, owned a remarkable horse named Clever Hans. Hans became world famous because he apparently could solve mathematical problems that involved decimals and fractions, tell time, and read, among other remarkable abilities. For example, someone (his trainer, as well as strangers) might ask Hans what 7 divided by 4 equals. Hans would tap the answer out with his hoof and receive a treat when he was correct, which was well over 90 percent of the time! A committee that included the noted German psychologist Carl Stumpf was appointed by the German government to study the phenomenal horse and prove his so-called abilities were nothing but a hoax. The committee completed their task and reported that although they were unable to prove Hans was receiving intentional cues, they remained unconvinced that he was able to solve such mathematical problems and complete the remarkable feats by using his cognitive processes. Stumpf's assistant, Oskar Pfungst, decided to continue investigating the phenomenal horse (Fernald, 1984). Pfungst conducted several experiments and concluded that when Hans could see the person asking the questions, then he was able to supply the correct answer. If Hans could not see the person asking the question, then his performance fell to near-zero levels. Pfungst was faced with two alternative explanations for the horse's abilities:
1. Hans understood the questions and was able to use cognitive processes (but only when he was able to see the questioner) to solve the problems.
2. The person asking the question was somehow inadvertently cueing the horse when to stop tapping at the appropriate moment (Watson, 1908).
Applying the Law of Parsimony, Pfungst chose the latter explanation and persisted in his investigations. He finally determined that almost everyone who asked questions of Hans made a minute upward movement of their head when the correct answer was reached. The horse used this cue to stop tapping and receive his treat (i.e., this was an instance of positive reinforcement).
If you apply the Law of Parsimony as you evaluate knowledge claims, you are well on your way to becoming a good psychological consumer. Some additional points to consider as you evaluate knowledge claims are covered in the next section.