I came across a blog post Instrumental interfaces, engaged interfaces a while back that left an impression on me. Recently, this mental model has popped up in my brain more frequently, so I spent some time reflecting on it. I do recommend the full post, but this excerpt summarizes the main concept well, that human interfaces serve two different kinds of uses:

Instrumental use. An instrumental user is goal-oriented. The user simply wants to get some good-enough solution to a problem they have, and couldn’t care less how it’s done.

Here’s a good litmus test to find out whether an interface is instrumental: If the user could press a magic button and have their task at hand completed instantly to their requirements, would they want that? If so, you are likely looking at an instrumental interface. A turn-by-turn nav, a food delivery app, and a job application form are all interfaces that are used almost exclusively in an instrumental way. Let’s call these instrumental interfaces.

Engaged use. Engaged users want to be intimately involved in the mechanics of an interface. They’re using the interface not just to check off a to-do item, but because they get some intrinsic value out of interacting with the interface, or they can only get what they want by deeply engaging with the interface’s domain of information.

A musical instrument, a board game, and a flash card set are all engaged interfaces, because they’re used almost exclusively for the intrinsic value of spending time using them. The user wants to feel the joy of performing music, not just listen to a track on a computer. They want to enjoy playing a board game, not just be handed a victory.

In short, the interface that you design should be reflective of the user’s motivation. What’s in it for them? Would they prefer a bike ride or teleportation? Most of us want to be in the “engaged” case, taking folks on a joyous bike ride, but instead we fall firmly on the “instrumental” side of things. It’s a simple thing that is easy to get wrong.

The kicker here is that AI is changing what solutions look like for instrumental interfaces. If the ideal interface is a magic button that teleports users to their objective, then AI is the closest thing we’ve encountered to said button.

And with that being said, the game hasn’t changed at it’s core. Instrumental interfaces are still as good as the underlying system allows them to be, but the ceiling has shifted quite a bit. So for builders, if we’re all trending towards designing a button, how do you differentiate from all the other “buttons” out there? A few angles come to mind:

  • Context: Your magic button has more information at it’s disposal.
  • Expertise: Your magic button better knows what to do with that information, how to execute.
  • UX: Your magic button is easier to understand, get started with, and use over time.

In this breakdown, context and expertise make the button better, while UX makes the button easier to press. If you draw this trend forward, than context and expertise matter more than ever, and UX, at least in the traditional sense, matters much less. I don’t think this happens overnight, but it’s provocative.

Let’s say we do end up in a world where headless, agent callable APIs and MCPs are the primary form factor of software. In this case, UX doesn’t disappear. Instead it re-centers around context acquisition and trust: how users interact with inputs, defaults, and feedback loops win out, not the steps along the way. The shape of solutions shift, the solution space shrinks, but the instrumental game stays the same.