I've come to avoid using the word "Simplicity" or its variants ("Simple," &c.) It means too many different things to different people.
For example, my original land-line phone was simple:
It's simple by eliminating extraneous use cases. It only handles one user scenario, the one that was the most common when it was invented. If we think of the number of affordances and the number of uses, this kind of simplicity lowers the number of affordances by lowering the number of uses. I call this kind of simplicity "Economical Design."
There's another kind of simple, a kind of band-aid simple. You start with something that can do everything, and add shortcuts for the most common use cases. For example, numeric keypads and function keys for turning your music up and down. Or on phones, you can have buttons for dialing your most frequent numbers and instead of pressing "*74" to redial, there's a "Redial" button:
This does make some things simpler, at the cost of increasing the number of affordances. You don't change the number of uses, you just bolt on special-case short-cuts to make some uses simpler. IMO, this reduces global simplicity but increases local simplicity. I call this kind of simplicity "Shortcut-Oriented Design."
And a third way of making things simple is to find a way to make a small number of affordances combine in some magical way to support a large number of uses. After sprinkling magic design pixie dust on the phone, we get:
I call this last example "Elegant Design." You pick your mental model and affordances in such a way that they scale extremely well in complexity. If you like recreational math, surreal numbers are a good example of a model that scales extremely well.
Now, this is not a universal design theory of everything, nor am I trying to present myself as an expert on telephony interfaces. But the general principle seems right, and it transfers well to programming languages and software: When some people say "Simple," they mean Does less. Others mean Makes the common use cases easy. And others mean Elegantly supports a large number of use cases with an interface and mental model that are simple to grasp.
Simplicity: Sometimes it's economical, sometimes it's shortcuts, and sometimes it's elegance.
