Difference between 揃う【そろう】 and 集まる【あつまる】


Could someone please explain a difference between 揃う【そろう】 and 集まる【あつまる】. I
dont think they are synonyms but can't see any difference between them?

Two example sentences:

> 駅前【えきまえ】に 人【ひと】が 集【あつ】まっています。 Lots of people are gathered in front of the
> station.
>
> 朝【あさ】は 家族【かぞく】全員【ぜんいん】が 揃【そろ】って 食事【しょくじ】します The whole family eats together
> in the morning.




Both 揃う and 集める include objects or living being coming together at one
location, but there's an important difference:

  * 集（め・ま)る is more or less a neutral collection
  * 揃う on the other hand includes a connotation of the collection being sufficient or complete 

You can 集める the pieces of a puzzle and end up with 1000 out of 1500, with 500
missing; but if the pieces of a puzzle 揃う, you've got all you need to complete
the puzzle.

If there's a real difference between two words A and B, I think it's important
to have a sentence with both words, such that A is true and B is not. So to
illustrate, here's a short sentence using both verbs:

> [members of an online community want to meet in real life]
>
> 全員揃うのは無理だろうけど、常連だけでせめて2、30人は集めたいよね
>
> It won't be possible for all of us to gather, but it would be nice if we
> could get 20-30 people with the regular users.

If people gather at a train station, they're just an unordered group of many
individuals. But if all members of the family come together, they're complete.

A few more examples to illustrate the difference:

揃う: gathered, and that's sufficient

  * 何しろ人的被害が多数に上る、最悪の条件がすべて揃っていると言えよう。
  * ひとり親より、両親が揃っていた方がいいと思っています。

集まる: gathered, but not yet enough

  * 多くの兵達が上甲板に集まっていたが、まだ部隊の集合は完了していない。
  * 二号の原稿はある程度集まっていたが、続刊を出すめどが立たなくなった。




揃う is used when _all_ the members of a certain group/family/section get
together. When used for inanimate objects, it means that everything that
composes a certain larger thing gets together.

>   * 揃った? Is everyone here?
>   * 部品が揃った All the pieces (of a machine, etc) are prepared.
>

You can use 全員(が) or すべて(が) with 揃う, but it's usually optional and doesn't
change the meaning of the sentence. 家族が揃う and 家族全員が揃う are semantically almost
the same.

集まる is used when random people/things are simply gathered.

