Coupling and Cohesion: The Two Principles for Effective Architecture

Every large system that spirals out of control starts the same way: small, functional, and deceptively simple. However, as the system evolves, things spiral out of control.

A feature is added here, a helper function squeezed there, and a “temporary” dependency for some urgent task that never gets removed. Months later, debugging requires going through five layers of indirection, and touching one module can break the entire system. 

Behind the scenes of that slow collapse, two invisible forces often play tug-of-war: coupling and cohesion.

Most developers first hear these terms in textbooks or blog posts, often lumped into a “good design” checklist. 

• High cohesion: good. 

• Loose coupling: also good. 

But beyond the concepts, the practical meaning often gets lost. What does coupling look like? When does cohesion break down in real teams? And why do some projects feel like a breeze to change, while others offer challenges with every pull request?

Coupling and cohesion aren’t abstract guidelines. They are practical engineering realities that define how easily code could evolve, how confidently teams could deploy, and how painful it becomes to onboard a new teammate or fix a bug under pressure.

In this article, we’ll attempt to understand coupling and cohesion in more realistic terms and how they might show up in different architectural styles and patterns.

Understanding Coupling