Accidental and Essential Complexity

Last updated Aug 5th, 2021
Determining if the complexity of a problem is related to the nature of the problem or related to the way that we approach solving it.

🌱 This blog post hasn't fully bloomed. It's very likely to change over the next little while because it's a little bit flawed. In fact, an old version of this post was titled "Absolute and Relative complexity". I then discovered that Ben Moseley wrote a famous paper written about this very phenomenon called, "Accidental and Essential Complexity". I'm re-writing this post to build on top of the existing philosophy using the terminology expressed there. The most up-to-date writing I have on this at the moment is in "Chapter 1 - Complexity & The World of Software Design" from This will eventually catch up

Ever seen a friend, coworker, or maybe even an accidental stranger- trying to solve a problem using a tool that you feel is completely unfit for the task at hand?

Maybe you've felt like a problem would be easier solved using a different tool, language, platform, or feature for the job.

It's frustrating. It's frustrating seeing someone introduce undue challenge for themselves when you feel like you know there's a better way.

In discussions about architecture, choosing a tech stack, and solving problems in general, I've started to use the terms "accidental complexity" and "essential complexity" more often. Maybe you will too.

Being able to point out accidental and essential complexity will enable you to:

Essential complexity

Essential complexity: When the complexity of the problem is related to the nature of the problem itself.

Let's face it. Some things in life are just inherently complex.

  • Making a vinyl-trading platform with lots of very specific domain-knowledge.
  • Architecting and constructing a house from scratch.
  • Using AI to write catchy pop music.
  • Coming up with a cure for cancer.

There's no easy answer to any of these things. Some of them don't even have an answer.

Often times though, we have a best practice. And a best practice acts as a close enough or the best that we can possibly do today. Best practices have considered all of the current options, and decided upon what the best approach is. Best practices are usually agreed upon by a larger community.

Here's an easy one.

The best practice for tying your shoes is to use your hands to tie your shoes into a knot. That's probably the easiest and most realistic way to tie our shoes, because well- mini robot butlers aren't really a thing yet. A way to make life harder and introduce accidental complexity is to force yourself to tie your shoes using only a pair of chopsticks, never touching your shoelaces with your hands.

Accidental complexity

Accidental complexity: When the complexity of solving the problem is directly related to the way that we have chosen to solve it, and less related to the nature of the problem itself.

When we take an approach to solving a problem that introduces more work or complexity for us, if not immediately, later on down the road, that's accidental complexity.

We don't often introduce accidental complexity purposefully. In software, sometimes it comes up when we:

  • Want to use a brand new programming language or tool to solve a project that it is not well-suited for
  • Are forced to use a particular tech stack
  • Are unaware of the best practices to solving this particular problem (and in turn, implement an anti-pattern)

Accidental complexity is introduced by failing to use best practices

When I was working on my first startup, I wrote the entire thing in vanilla Node.js. Over time, we started to get more and more business logic complexity added to the app. Eventually, I found myself in a position where it was impossible for me to add new code without breaking old stuff.

It was a huge mess because I had designed it with CRUD & MVC (also known as a Transaction Script) where the problem really needed a more robust solution.

In this scenario, the challenge was to build a large-scale business logic-heavy enterprise application.

The best practices for that task are to use Domain-Driven Design, separate your concerns using the clean/hexagonal architecture, write tests, and implement design patterns when necessary.

It turns out that doing all of these things with JavaScript is hard. Harder than it needs to be. There are several reasons why, and I explain why in detail here, but ultimately, it's the lack of a language concept to express abstractions (interfaces and abstract classes). Without abstractions and a type system, implementing contractual software design is harder in JavaScript.

That was the main reason why I made the move to TypeScript for that project; because the best practices for a large-scale business logic-heavy enterprise application were easier to implement in TypeScript than in JavaScript.

Yes, it was a challenge to learn and migrate to TypeScript. But that challenge was guided towards implementing the best practices that the problem afforded. Not all projects have the same needs as a large-scale enterprise app.

Sometimes best practices are a lot of work

I'm not gonna lie. Writing testable code, using DDD, and clean architecture is a lot of work. But if you're working on a project that needs that, and you're able to identify that, then it's the best path we have to the right way to do things.

Anti-patterns can introduce essential complexity

In the evolution of bad code, it starts with code smells. Code smells are indications that something might be wrong with the way we've designed our code and that we should probably take a better look at it.

That's the first step towards bad code, and it's not purposeful. These things just happen sometimes. If we can catch it, that's great. We can refactor and clean up code before it becomes a problem.

class User {
  // Wait. Why would we need to pass in a "logger" object to create a user?
  // A logger is an "infrastructural" cross-cutting concern, and it definitely 
  // doesn't belong in our user factory method.
  // Also, this parameter list will only increase as we add more things to create
  // the user. We should use an object instead.
  public static  createUser (userName, password, firstName, lastName, logger) {

An anti-pattern, however, is a little bit more aggressive. An anti-pattern is deliberate approach to solving a problem in a way that goes against best practices.

Anti-patterns have the potential to introduce essential complexity.

Anti-pattern example: Duck-typing with JavaScript

Problem: To prevent developers from passing in invalid objects.

Let's say that we want to create slugs for blog posts using the following function.

// Returns a slug like: "2020/02/12/accidental-complexity-212312
function createSlug (post) {
  return createDateString(post.postedDate) + "/" 
    + createSlugFromTitle(post.title) + "-"
    + createRandomNumber();

The function expects that we're going to pass in a Post object that has postedDate and title attributes.

But developers keep on passing in the title of the post as a string like so:

const post = "Accidental and Essential Complexity";
const slug = createSlug(post) // ERROR

This is a silly problem. But on projects that are substantially large, it's pretty common to see. Especially if you're not familiar with the entire codebase.

Essential complexity: Need to signal to clients that use the API that the method requires a post object with postedDate and title, and enforce that.

Accidental complexity: Using JavaScript,

  • For API clients, you need to know the internals of every method. You can't rely on intention revealing interfaces alone.
  • For API authors, you need to use duck-typing and throw errors.
  • For API authors, you need to write more comments so that developers know how to use the API. The function signature is not enough to express valid use.
 * @desc Creates a slug. You need to pass in a post object with `postedDate`
 * and `title` to create it.

function createSlug (post) {
  if (!!post.postedDate === false || isADate(post.postedDate)) {
    throw new Error("Need to provide a post object with date as 'postedDate'")
  if (!!post.title === false || typeof post.title !== "string") {
    throw new Error("Need to provide a post object with a string title.")

  // Also, we would need to include the post title's validation logic here as well
  // which may include making sure that the title is a certain length.

  return createDateString(post.postedDate) + "/" 
    + createSlugFromTitle(post.title) + "-"
    + createRandomNumber();

Best practice solutions:

  • Use a statically-typed language to indicate and enforce valid API usage.
function createSlug (post: Post) {  return createDateString(post.postedDate) + "/" 
    + createSlugFromTitle(post.title) + "-"
    + createRandomNumber();

Breaking best practices and implementing anti-patterns

Implementing best practices and avoiding anti-patterns will get us where we need to go in the long run, but will often require some more upfront work.

I think it's occasionally OK to break best practices and implement anti-patterns in order to go a little faster.

I give it my blessing in one condition...

Know what the rules (best practices) are before you decide to break 'em.

I take shortcuts all the time. But I try to always know what the implications are first.


No Silver Bullets - Accidental and Essential Complexity

Shortly after this post was released to the interwebs, someone kindly pointed me to the "No Silver Bullet – Essence and Accident in Software Engineering" Wikipedia page. Funny. The fact that I had arrived at the concept of accidental and essential complexity myself, yet was already well-researched and discussed as essential and accidental complexity, reinforces the following statement:

"Not a lot has changed about the fundamentals of software design over the past 20 years, but there's a huge lack of training on it" - me, via

If you're interested in learning more about this subject, I suggest checking out this paper called "Out of the Tar Pit" by Ben Moseley.

It builds on top of the classic paper about software complexity originally discussed by Fred Brooks in 1986. It's very well put together and worth your time. Consider reading the first half at least.


In summary, ask yourself if the problem is hard because it's a hard problem, or if you're making it hard by not following best practices.


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About the author

Khalil Stemmler,
Software Essentialist ⚑

I'm Khalil. I turn code-first developers into confident crafters without having to buy, read & digest hundreds of complex programming books. Using Software Essentialism, my philosophy of software design, I coach developers through boredom, impostor syndrome, and a lack of direction to master software design and architecture. Mastery though, is not the end goal. It is merely a step towards your Inward Pull.

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