# Metaphors and learned gestures · Invisible details Rauno Freiberg opens [Invisible Details of Interaction Design](https://rauno.me/craft/interaction-design) (July 2023) with an admission. Design can feel like there is no science to it, “only feel and intuition,” and even researchers treat the practice as a black box (he cites a 2011 CHI paper by Goodman, Stolterman, and Wakkary). The web returns recycled personas and UI/UX Venn diagrams; the substance shows itself only to people willing to read obscure papers or replay hundreds of slow motion screen recordings. ### Observation, not guidelines The essay is “not a tutorial nor a collection of guidelines,” but an observation of details in interactions he uses often and rarely thinks about. His revelations surface from making something, then going for a walk. Like recreating interfaces, this reflection builds design intuition and vocabulary. Source The black box claim is footnoted to E. Goodman, E. Stolterman, and R. Wakkary, Understanding Interaction Design Practices (CHI 2011). The resources list also names Apple’s 2018 WWDC session Designing Fluid Interfaces, Jason Yuan’s MercuryOS, and Brian Lovin’s App Dissection. His definition is short. **Interaction design** (Interaction design is an artform to make experiences that fluidly respond to human intent.) is “an artform to make experiences that fluidly respond to human intent.” It is not painting: people use a product to get something done, so beauty of form is not enough, and the satisfaction comes from a holistic balance of form and function. His questions are this chapter’s: when does a swipe trigger an action, do gestures retain momentum, what happens when a finger covers content, how can an interface predict intent from context. ### Two gestures teach the rest The first answer is metaphor. “Great interaction design rewards learning by **reusing metaphors** (Great interaction design rewards learning by reusing metaphors.).” Most touch interfaces need two gestures, tapping and swiping, and on iOS the only one you are explicitly taught is swiping up to open. That one swipe unlocks much of the interface. The sliding motion is also structural: the interface is stacked layers, like a deck of cards, and swiping down reveals layers of system functionality. The knowledge compounds across the Apple ecosystem, and every surface that honours the metaphor costs nothing to learn. ### Borrowing properties, not looks Why does swiping horizontally move between pages? Because that is how we have interfaced with books for thousands of years. The metaphor brings real-world properties with it, and the one he singles out is **interruptability** (Great interactions are modeled after properties from the real world, like interruptability.). Flipping a page is obviously interruptible, which sounds silly until you imagine the page turn as an animation you had to wait for. Pinching is subtler. Zooming is an act of precision, adjusting the amount of detail visible, and the interface first has to establish an anchor point, which is easier and more precise to pick with the fingers pinched together. Starting apart usually means zooming out, where the exact origin matters less. Deliberate precision wants two fingers close together, “kind of like grabbing an object.” ### The question to ask He closes with the sentence that names the essay: hundreds of design decisions are made by someone obsessing over the tiniest margins so that, when they work, nobody has to think about them. Many tap into instinctive behaviour. So before you invent a gesture or a transition, ask which metaphor it borrows and whether it keeps that metaphor’s properties. A swipe that cannot be interrupted, a layer that does not slide, a zoom with no anchor: each breaks a promise the user did not know they were relying on.