One of the first posts I read at Psychology Today when I started blogging there was written by a young man who argued strenuously that psychologists should endorse only “testable ideas and theories,” and cast out the rest. I applaud the notion that we should support our ideas and theories with evidence. But at the same time I’m kind of concerned about this contention that only psychometric tests provide valid evidence, because I know that no matter how absurd a statement is, if it begins to circulate (as this idea does in some graduate programs of education and psychology) more and more people will start to believe it.
The obvious fact is that most of what anybody knows is not based on testable propositions, if by “testable” we mean a rigorous process of devising methods for isolating certain independent variables and seeing how they react to controlled variations. You know the driver ahead of you is not paying attention, that your child is stretching the truth, that this tie won’t go with that jacket, etc. All of this knowledge is based on evidence, but not upon evaluating testable propositions. In the last fifty years or so, there has been a tendency in some quarters to claim that the only real knowledge is that which can be backed up by testable, preferably quantitative evidence. That idea is so obviously stupid that I don’t really know where to begin in disputing it.
Now, in saying that this is a stupid idea, I do not mean for a moment to say that those who express it are themselves lacking in intelligence. Rather, they are repeating what they have been told, which is something that all human beings are very likely to do. And that’s the very reason that it is best to be vigilant about stupid ideas.
By all means, let’s use scientific methods whenever possible to figure out the sorts of things that can be tested through controlled experiments or the quantitative assessment of careful observations. But it does not follow from this commitment that controlled tests provide the only sort of valid evidence. If a psychotherapist with decades of clinical experience is able to offer insight into a patient’s behavior based on subtle factors such as facial expression and what the patient said two weeks ago, that insight may be based on evidence as well, even though it’s not “testable.” Can you provide a testable explanation for why the Axis powers were defeated in the Second World War? Does that mean that some explanations for the course of the war aren’t supported by better evidence than others?
There may be seemingly sensible people around you who say that the only real knowledge is that which can be supported with quantitative evidence, but that doesn’t make it true. This is an affront to common sense, and if you accept this statement, your intellect will be thereby impoverished.
