According to the dictionary definitions, "complex" and "complicated" almost always can interchange when it comes to "difficulties" that you deal with in a situation or problem. Consequently, it should come as no surprise that the two nouns "complexity" and "complication" should also be nearly the same things. But perhaps they are not!


  • The state of having many parts and being difficult to understand or find an answer to.


  • Something that makes a situation more difficult.

To elaborate my meaning, I would like to raise two examples here:

    1. The complexity of urban life is increasing day to day.

Ngram shows that, the word "complication" cannot be substituted for "complexity" in this sense or it is used very rarely.

For more clarification, let me bring up another example:

    1. The complexities of human relationships have become a quite significant and serious issue today.

Again, Ngram reveals that these two cannot be replaced or at least "complication" is not used much in this sense.

Now, I wonder if it is a matter of formality where Ngram cannot look up informal cases, or it is a matter of fixed phrases? Please do me a favor and help me with this question.

1 Answer 1


I think Ngram may be leading you astray.

I would argue that The complications of urban life are increasing day by day is perfectly normal usage, though note that I had to amend it slightly: changing is to are.

I would also argue that The complications of human relationships ... is also perfectly valid usage, though the meaning has changed quite a bit.

  • Thank you @Mile Brockington, but please let me ask some questions. 1 I was wondering why did you make the first example of mine using the plural form of "complication" while "complexity" was singular? --- 2 As for my second example, after using "complication", you mentioned that: "...though the meaning has changed quite a bit." I was wondering why?
    – A-friend
    Commented Sep 24, 2019 at 16:21
  • 1
    @Seamus has done a good job of explaining your q.2 - complexity and complication come from the same root, so have similar meanings, but when learning English you should be aware that this is always a red-flag: some words in English have almost exactly the same meaning, but came from different sources. When they have the same root, you can be sure that there are significant differences in the way that they are actually used by native speakers.
    – MikeB
    Commented Sep 25, 2019 at 9:50
  • For your q.1 I really just have to say "because that's the way it is" - in this context complications are plural in reality - a human relationship with only one single complication would be rare indeed!
    – MikeB
    Commented Sep 25, 2019 at 9:53
  • Well @Mike Brockington the I was wondering why you have used "complexity" rather than "complexities"? Or I can use "complexities" as well?
    – A-friend
    Commented Sep 25, 2019 at 12:31
  • 2
    complexities (plural) - yes, no problem. But as noted before, there are subtle differences in nuance.
    – MikeB
    Commented Sep 25, 2019 at 13:44

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