Part 1 - Designing with the brain in mind and how Gestalt principles shape what we see (The law of similarity)
The mind behind the eye
As designers, our work lives at the intersection of art, technology and psychology. One of the most powerful psychological frameworks we can apply to our practice is Gestalt theory, a set of principles developed by early 20th-century psychologists to explain how humans organise visual information.
The core idea behind Gestalt is simple, but profound: the whole is perceived differently than the sum of its parts. Our brains instinctively seek patterns and relationships, and we do this so automatically that we’re often unaware of it. Understanding how these patterns work gives us more than just design tools, it gives us insight into how people actually experience what we create.
What are Gestalt principles?
Gestalt principles describe how we naturally group visual elements into unified wholes. These principles help explain why we instinctively see structure in the visual chaos around us, whether in nature or on a webpage.
The major principles include:
Similarity
Continuation
Closure
Proximity
Figure/Ground
Symmetry and order
Each one reflects a fundamental cognitive process. In this article, we’ll focus on the law of similarity, and explore how it can make our work more intuitive, persuasive and effective.
The law of similarity and how we connect what looks alike
The law of similarity states that we tend to group visual elements that share similar characteristics, such as shape, colour, size or orientation, and perceive them as part of the same group or pattern.
This grouping happens at the subconscious level. The eye picks up on the similarities, and the brain automatically forms connections between those elements. Whether the items are close together or far apart, their resemblance is enough to trigger the effect.
This is why even basic changes, a different shade, font weight, or icon style, can significantly alter how a design is read.
Why this matters for design
Designers are not just decorators; we are translators. We take abstract goals, communicate this message, guide the user to that action, and translate them into visual systems that the brain can process quickly and effortlessly.
Understanding similarity allows us to:
Create hierarchy without extra lines or boxes
Guide user attention without shouting
Establish patterns that are easy to learn and navigate
Break patterns intentionally to draw focus
Let’s look at how this works in a few real design contexts.
Links and navigation
On almost any website, you know what a link looks like, typically blue, underlined text. This is similarity at work: uniform style equals uniform function. If one link looks different from the others, users may not realise it's clickable, or worse, think it's broken.
Likewise, navigation menus rely on consistency. If a horizontal nav bar uses identical buttons for each item, your brain groups them as a cohesive set, even if they point to wildly different pages. If one looks different (and it's not a call-to-action), the inconsistency risks confusion.
Content patterns
We often apply similarity in editorial content to reinforce meaning before the user even reads. Quotes, for example, are often styled with larger type, italics, and an offset layout. This pattern is familiar, so users recognise it instantly, even across different sites. This is cross-site pattern recognition driven by similarity.
Breaking this pattern say, by styling a key marketing message with a contrasting format, grabs attention. This is where understanding the law helps us not only establish harmony, but also disrupt it deliberately when needed.
Headers and structure
Good headers don’t just separate sections, they help users scan, absorb and anticipate. A visual hierarchy created by consistent font size, colour and spacing helps establish rhythm and flow. Without it, a page becomes a wall of text, demanding more cognitive load.
Similarity helps users recognise where they are and where they’re going, even if they’re not reading every word.
Cognitive fluency and reducing mental load
The beauty of similarity lies in cognitive efficiency. When design elements look and behave in consistent ways, the brain doesn’t have to work as hard to decode them. This “fluency” makes interfaces feel intuitive, even when they’re complex underneath.
In contrast, inconsistency creates doubt. If buttons, icons or headings don’t follow a recognisable visual pattern, users must stop and ask: Is this clickable? Is this important? Is this related to that? Every one of those questions adds friction.
A designer’s eye is a behavioural tool
Designing with Gestalt principles means working with the way the brain wants to see. That doesn’t mean your layouts must be rigid or repetitive, it means knowing when and how to apply consistency, and when to break it.
Whether we’re building a dashboard, app, or editorial site, we have the power to shape perception. And when we respect how perception works, our designs become more than aesthetic, they become effective.
This is psychology with purpose
Gestalt theory isn’t just academic. It gives us a playbook for designing systems users can trust, understand and enjoy. The law of similarity teaches us that even the smallest design choices, a typeface, a button colour, a shape, can change how someone understands what they’re seeing.
When we apply this principle thoughtfully, we reduce friction, guide action and build meaning. And that’s not just good design, it’s good communication.
Next up is ‘continuation and closure’
This is the first in a series I’m writing about where I explore Gestalt principles in design. In the next article, we’ll look at the law of continuation and how the brain loves to follow lines, paths and sequences, and how we can use that to guide users more naturally through content and interaction.
Thanks again for reading and enjoy the rest of your day!
