From time to time I have an error in a computer system.

What is better to say:

  • The error happened again yesterday.
  • The error occurred again yesterday.

Is there a semantic difference between the two sentences?

Does one of the two carry a kind of surprise? I want to express, it is not surprising, it just happened again.

2 Answers 2


It's an interesting question. As @Mistu4u mentioned, the formal definitions of both words are similar.
There are some differences, however:

Happen — something random to take place;
Occur — something to become observable; in a certain moment; an event or a process;

The difference is even more evident if you notice that occur is relative to current as they both came from Latin currere "to run".

So, I would use occur in the following contexts:

...and happen in the following contexts:

  • Informal context;
  • Rough time or place;
  • Random events, usually without being planned;

As usual, you can step off these recommendations if you need to convey your attitude about what you are speaking about.

  • 1
    I feel like "occur" can use for the existence of non-event things ("non-happenings", like a physical thing for example) too, as in "a sound occurs in this language" or "mosques don't occur naturally". Feb 7, 2018 at 8:29
  • @Vun-HughVaw That's because the word “to occur” has another sense that “to happen” doesn't have: “to exist or be found to be present in a place or under a particular set of conditions.” Substantive things do not happen, but occur. May 27, 2019 at 20:42

Occur and Happen are synonymous in this context. So you can use any of them. By the way, the sense you want to mean can also be expressed with Recur. It means to "occur again periodically or repeatedly:"

  • Yes, but "synonymous" in OP's context. You can't use "happen" in, for example, "The idea did occur to me that there might be a missing caveat there". Feb 6, 2013 at 19:20
  • @FumbleFingers, Occur to is definitely different from occur, isn't it?
    – Mistu4u
    Feb 6, 2013 at 19:25
  • 4
    When talking about synonymous words, it's usually good to add a phrase such as "in this context." Most words have multiple uses, and it's rare to find a synonym that can be substituted in all instances. Even though "in this context" may seem obvious, you don't want your answer to create the false impression that the two words are always interchangeable. I might ask FumbleFingers, "What's happening?" but I wouldn't ask, "What's occurring?"
    – J.R.
    Feb 6, 2013 at 19:38
  • 2
    @Mistu4u: What J.R. said. I wasn't seriously criticising your answer (I did upvote it, after all! :). Just pointing out that whereas you and I might know that occur to has it's own special meaning, it's quite likely that on this site, many others won't know that. Feb 6, 2013 at 21:35
  • @J.R.: Actually, I have noticed an upsurge in "What's occurring?" being used as a quirky/facetious variant of "Wassup?" in recent years. But as with so many aspects of language use, it's often okay to deliberately break the rules for effect provided you actually know the rules. If you don't (more correctly, if others might think you don't), you risk being perceived as ignorant. Feb 6, 2013 at 21:40

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