Blog Posts from August, 2006

Intuition and Common Sense

Tuesday, August 22nd, 2006

James Bach recently blogged on the notion of intution and common sense being considered harmful. You can read his post here:

Merriam-Webster Online says of “intuition”:


Etymology: Middle English intuycyon, from Late Latin intuition-, intuitio act of contemplating, from Latin intuEri to look at, contemplate, from in- + tuEri to look at
1 : quick and ready insight
2 a : immediate apprehension or cognition b : knowledge or conviction gained by intuition c : the power or faculty of attaining to direct knowledge or cognition without evident rational thought and inference


The word “evident” in the second definition struck me as interesting. It doesn’t say that intuition is magic, or without rational thought or inference; merely that the rational thought or inference isn’t evident.

A huge part of the mission of skilled tester, I believe, is to build credibilty by identifying and communicating our skills–which include developing rationally thoughtful inferences–to ourselves and to others. In order to do this, we need to make our thought processes visible and evident, and to identify and articulate what is common and sensible about our common sense. By the same token, when we’re fooled by a puzzle or a bug, it’s important to identify how our intuition and our sensibility could be sharpened.

Here’s an example. A colleague in Brazil gave me this puzzle to solve:

You are down the hall and around the corner from a room. The door to the room is closed, and the lights inside are off. There are three switches on the wall in front of you. One of them controls a lamp in the room. You must find out which switch controls that lamp, but you may only enter the room once (and opening the door counts as entering the room). No light leaks through the door (which closes as soon as you let go of it), and there is no other door, nor is there a window. There is no one else around to help you, and there are no tools, mirrors, or cameras available. How do you figure out which switch controls the lamp?

If you can’t solve the puzzle, the answer appears below. Hints and the answer follow, so if you don’t want to spoil the fun of solving it yourself, stop reading now!

I didn’t solve the puzzle, but as soon as my colleague began her explanation, I was able to leap to the answer without her finishing.

Hint 1: For many puzzles, it’s tempting to consider logic and tools. Logic will help here, but only to some degree, and tools are necessary.

Hint 2: The reminder that I needed was to consider more sensory modes–an important general systems principle.

Hint 3: I thought about sight and hearing, but I failed to consider the other three of the five senses.

Answer: Turn on one of the switches, and leave it on for a minute or so. Turn it off, then turn on one of the other two switches, and enter the room. If the lamp is on when you enter the room, you’ve found the right switch. If the lamp is off, touch the bulb. If it’s warm, the first switch controls the lamp. If it’s cool, the switch that has never been on controls the lamp.

I don’t feel that I’m very good at this kind of puzzle, and I’m often startled by people who can get the right answer right away. They usually explain that the answer is “obvious” to them. Obvious is my favourite one-word tautology: something is obvious to someone for whom it is obvious, and not obvious to someone for whom it is not obvious. I think that there’s a different explanation: that people who solve this puzzle without hints or help consider those different sensory modes, and those of us who don’t consider them get stuck on the puzzle. So, here’s a new puzzle solving heuristic: consider all of the senses as a means of helping find a solution to a problem.

I don’ t mind following James’ lead and banishing “intuition” and “common sense” from referring to my own thought processes, but I would like to begin using the words as trigger heuristics when I hear them from others. When I hear the words, I’d like them to prompt me to try to figure out the rational thought that people are perfoming and the inferences that they’re making, and to gather evidence that that’s what’s going on. I want to develop the skill of immediate apprehension and cognition by making invisible assumptions and heuristics as visible as possible.

That’s part of what being a tester is all about, isn’t it?