A few years ago, I was discussing a new product feature with a colleague. What they said in that conversation had me momentarily stunned. I didn’t know how to respond.

We were discussing a new design and debating whether or not to include a certain button. I wanted to add it and they didn’t. After hearing many protests about how adding this button would increase the complexity of the interface, I decided to try to understand their motivations. I asked a direct question: “do you really think that the fewer buttons a product has, the simpler it is?” Their response was an emphatic “yes”.

I didn’t know how to respond—I was disappointed. When first asked the question, I think many people may side with my colleague. I’d like to explain why I thought they were wrong, and why I felt so uncomfortable.

An interface can be difficult to use if it has too few controls. When there are not enough controls, each control must take responsibility for multiple functions.

Imagine a simple product that opens and closes a garage door. One version of this product’s control interface provides three buttons - open, close, and stop. Another version has one button. Which do you think is simpler for people to understand and use?

The one-button interface makes the function of the button at any time ambiguous. Consider the case when the door is closed. Presumably if I press the button the door will open. But what happens if I press the button while the door is opening? Maybe the door will stop. Now, what happens when I press the button again? Does the door continue opening, or does it start to close? What if when I press the button while the door is moving, it doesn’t stop, but instead starts moving in the other direction? Unless you memorise what the button does in each state, the intended function is not clear or obvious. The functionality of the product is so simple, yet by overloading one button it becomes unnecessarily complicated.

The three-button interface, however, is remarkable in its simplicity. Press open and the door will open. Press stop and a moving door will stop. Press close and the door will close. It’s got more buttons, but it’s much clearer.

I want to be clear that I’m not supporting the opposite position – I don’t think that the more buttons an interface has, the easier it is to use. I don’t think you should make statements like “it has fewer buttons, so it’s simpler” or “it has more buttons, so it’s simpler”. These cases are rarely binary. Every situation needs appropriate thought and a considered response.

As a different example, think about the iPhone. This seems to be used often as an example of the pinnacle of simplicity: “it’s only got one button – one Button! It’s so simple.” Despite the fact that the phone actually has more than one physical control (home button, power button, volume buttons, and possibly a mute/lock switch), it’s a pretty useless device if that is the extent of the controls to which you have access. As soon as you turn the device on, the screen fills with many rich and varied controls, all hopefully designed with an appropriate form and layout to make their function clear.

To me, the beauty and simplicity of devices like the iPhone, is that its interface adapts appropriately to the many and varied functions that it is asked to provide. If the iPhone did only have a single button, and that button somehow had to control every function the iPhone could provide, it would be far from a simple device.

If you calculate complexity based on the number of buttons, or any type of control, that an interface has, you might consider the iPhone to be the most complicated device in existence. Many people find it to be the opposite.