The Intentional Stance

A big idea from Dan Dennett

In this post I'm going to discuss some good ideas by the philosopher Dan Dennett. Namely that we should use different perspectives or "stances" to understand systems with differing degrees of complexity and intelligence. He describes three levels of analysis: the physical stance, the design stance, and the intentional stance.

All of them are very common sense ways of thinking, and will seem very familiar once they are described. They are all used extensively in everyday life and science. Of the three, the first one (the physical stance), tends to get the most respect as a legitimately sciencey way of doing things. The second one (the design stance) tends to get viewed with some suspicion, and the third is sometimes considered to be fallacious. According to Dennett, each perspective or level of analysis has its own costs and benefits, and is appropriate for different kinds of jobs. I agree, and think that the intentional stance is often underutilized as a very common sense and effective way to understand pain and motor control.

The Physical Stance

Imagine you wanted to predict the result of a very simple event, like releasing a rock from your hand. Using your knowledge about the laws of nature, you would guess that the rock will fall down, not rise up. Dennett calls this thinking process the “physical stance” because it views the object whose behavior is to be predicted as being under control of physical laws. This perspective affords the potential for amazing precision in your predictions. If you have accurate information about the important variables - the angle and velocity of the rock's release, etc, you can determine almost exactly what it will do after leaving your hand. Physicists, chemists and engineers primarily use the physical stance in their work. A lot of what we think of as “science” is applying the physical stance.

The Design Stance

Now imagine you release a bird from your hand. Applying the physical stance is no longer very practical. Even though the bird is made of physical stuff that must obey the laws of physics and chemistry, there are so many parts to the bird, and they all interact in such complex ways, that using the physical stance is, as a practical matter, impossible.

To predict the behavior of the bird, we use the “design stance.” We know that birds are “designed” to fly, so we assume it will act in accordance with this design when released.

We use the design stance all the time to predict the behavior of machines. When I press the start button on my coffeemaker, I predict it will start making coffee and not blow up, because my coffee maker was designed to make coffee, and not blow up. At least I assume this is the case, and I could be wrong. Maybe the coffee maker was actually designed by an evil genius, or maybe its design is now broken. To know for sure, I would need to take it apart and apply more of a “physical stance” mode of analysis. But this is impractical.

In biology, the design stance is ubiquitous. It involves the recognition that organs have functions and purposes. The heart was “designed” to pump blood; the kidney is a filter; the “purpose” of the lungs is delivery of oxygen to working muscles, so they can do their “job” of contracting to “help” us move. We predict that these organs will in most cases act in accordance with these purposes. For example, when muscles are working hard, we are unsurprised to learn that the lungs will also start taking in more oxygen to “help” them. These ideas about function and purpose and design are essential to a scientific understanding of the body, even though they involve concepts that are somewhat ambiguous, and not subject to precise measurement or proof. What’s the purpose of the appendix? We don’t know.

(By the way, all the scare quotes used above are there to acknowledge that things like hearts and lungs aren't “designed” in the same way that DVD players are, nor do they have “purposes” in the same way that people do. But Dennett would say the difference is smaller than you think, and one of degree. If you want more information on that, try some of Dennett’s books.)

One of the cool things about the design stance is that once you know what something is designed to do, you can make accurate predictions about its behavior without knowing anything at all about its inner workings. I don’t need to understand electronics to guess what a DVD player will do when I insert a DVD. And I don’t need to know exercise physiology to know that my body will probably adapt to get better at withstanding the physical stress of certain kinds exercise - that’s what its designed to do!