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According to Lexico, the word simultaneously means "At the same time".

And the word concurrently means "Existing, happening, or done at the same time".

And the word (phrase?) at the same time means "Simultaneously".

So then how do you use these words differently? I feel that concurrently is slightly different than the others, but I can't find any difference between At the same time and Simultaneously, even the dictionary says it's same. Still, I often see they're used differently:

  • It was simultaneously frightening and annoying.
  • He was given two prison sentences, to run concurrently.
  • He looked hurt and angry at the same time.

I think the first one and third one is interchangeable if we change the order of some words, but I don't think second one is interchangeable(But I don't know why, I just feel that it isn't).

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  • Have you tried other sources? Please share your findings
    – gotube ♦
    Commented Sep 16, 2021 at 7:06
  • I've checked them on Lexico, cambridge, and my own paper dictionary... Which led to same consequence.
    – Skye-AT
    Commented Sep 16, 2021 at 7:14
  • Jack's answer is my answer
    – gotube ♦
    Commented Sep 16, 2021 at 7:21
  • 2
    Example: "simultaneous equations" can be replaced by neither "concurrent equations" nor "at the same time equations".
    – Display Name
    Commented Sep 17, 2021 at 12:18

4 Answers 4

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Concurrently refers to coincident or overlapping spans of time, as in the example of the two prison sentences.

Simultaneously can refer to a single moment in time.

The phrase at the same time is a more general phrase that describes both of the other two terms.

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  • So can I think that simultaneously is more precise than at the same time?
    – Skye-AT
    Commented Sep 16, 2021 at 7:17
  • 7
    I would say it's more specific.
    – Jack O'Flaherty
    Commented Sep 16, 2021 at 7:39
  • I'd would say it's its definition. simultaneously == at the same time. In fact @Skye-AT you've pointed out it's a definition in at least one source. To others, in this context what is the difference between specificity and precision?
    – mcalex
    Commented Sep 17, 2021 at 5:02
  • @mcalex To be honest, I don't even know if I pointed out that it's "definition". I now kind of understand the difference of them, but still don't really know whether should I use "at the same time" or "simultaneously"... If I'm understanding it correctly, when I need precise timing, then it's better to use simultaneously. Still, according to this answer,("The phrase at the same time is a more general phrase that describes both of the other two terms.") I can still use at the same time in that context. So... preference, I guess?
    – Skye-AT
    Commented Sep 17, 2021 at 9:17
  • @Skye-AT you said you looked it up and lexico told what it means - that's a definition. Yes the choice is up to you; issues such as word count, audience level and prior use of either term could all affect the decision.
    – mcalex
    Commented Sep 17, 2021 at 9:25
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In Latin, 'simul' (simultaneous) means "together, at the same time".

In Latin, 'concurrentem' (concurrent) means "to happen at the same time".

Concurrent connotes there being no relation other than a temporal one.

Simultaneous DOES connote there being a relation other than just temporally.

You could be simultaneously babysitting and working from home. And in all likelihood, you'd be doing so concurrently with some of your co-workers. If two or more of you were doing so simultaneously, then you'd have to be in the same building otherwise you're not "together".

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  • 9
    The meaning of an English word derived from a Latin word can vary considerably from the meaning of the original Latin word. English has taken the "at the same time" meaning from simul but has discarded the connotation "together." The idea that simultaneous events must occur in the same building is simply absurd.
    – David K
    Commented Sep 17, 2021 at 12:21
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    @DavidK ... assuming that is the intended meaning of together. do also note that together often means at the same time instead of at the same place... in which case there's not much difference according to these definitions
    – somebody
    Commented Sep 17, 2021 at 18:41
  • well... i guess that is more the fault of the answer though
    – somebody
    Commented Sep 17, 2021 at 18:41
  • @somebody True, it could be an overinterpretation of the translation of simul to English, rather than a shift in the meaning of the word. I do not know the appropriate Latin usage of simul, so I don't actually know where this answer went astray -- but I still disagree with its prescription for English usage. :-)
    – David K
    Commented Sep 17, 2021 at 23:57
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  • Concurrently brings the notion of competition for a resource that cannot be shared or which can not be acted upon in diverging ways. For example two persons concurrently pushing a door handle at the same time, can be said they use the door concurrently.
  • Simultaneously means a single moment in time with multiple things happening in perfect synchronicity.
  • At the same time is less precise, as it highlights a time span where multiple not necessarily related events happens. The time span is what binds those otherwise weakly related events.
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There is an appreciation of precision in the use of "simultaneously" not shared by the others.

(One thing simultaneously happening with another at that same moment)

You opened the office door and simultaneously the mirror that was leaning against it came crashing down.

Whereas "at the same time" usually applies to actions that are generally together, not necessarily dependent but may be related.

(One thing happening the same time as another)

Your boss looked up meaningfully at the clock at the same time that you entered the office.

Concurrently is neither of the above.

(One thing immediately following the other)

Your boss is serving two prison sentences concurrently - one for failing to grab a mirror that fell on an employee, and the other for possession of a stolen clock.

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    "One thing immediately following the other"? The two prison sentences started simultaneously. Neither one follows the other. If one followed the other they would be consecutive sentences and your boss would be in prison longer than if he'd been allowed to serve them consecutively.
    – David K
    Commented Sep 18, 2021 at 0:01
  • @DavidK Thank you for correcting that "like a boss"! (Even though the accidental word swap at the end may have thrown some off.)
    – Chaya Cooper
    Commented Apr 1, 2023 at 21:34
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    @ChayaCooper "... longer than if he'd been allowed to serve them concurrently." Yes! You're right, of course: the final "consecutively" in my previous comment absolutely was an accident.
    – David K
    Commented Apr 1, 2023 at 22:01

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