happen

occur, happen, take place

三者都表示“发生”，都是不及物动词。
happen: 指“偶然发生”时，主语为“事”；当主语是“人”时，意为“碰巧”。happen to sb．／sth． 指不好的事情发生在某人（物）身上。

• he happened to know the place.
  他碰巧知道那个地方。

occur: 指“发生”时可与 happen 换用，但后接to sb．／sth．时，两者含义不同：；occur to sb．／sth． 指“某种思想等呈现于某人的知觉中”。

• didn’t it occur to you to phone them about it?
  你难道就没想过给他们打个电话？

take place: 表示“发生”，可与 happen 或occur换用，但其后面一般不接 to sb．／sth．结构；指必然会发生的事情时，多用 take place；此外take place 还可表示“举行某种活动”。

• in 1919, the may 4th movement took place in china.
  一九一九年，中国发生了五四运动。

动词 happen:

1. come to pass
   同义词：hap, go on, pass off, occur, pass, fall out, come about, take place
2. happen, occur, or be the case in the course of events or by chance (Santayana)
   同义词：befall, bechance
3. chance to be or do something, without intention or causation
4. come into being; become reality
   同义词：materialize, materialise
5. come upon, as if by accident; meet with
   同义词：find, chance, bump, encounter

1. What happened when you told him the news?
   你告诉他这消息时，他有何反应?
2. I happened on just the thing I'd been looking for.
   我偶然发现了我一直在寻找的东西。
3. I happened to see her yesterday.
   我昨天碰巧见到她。
4. The accident happened at six o'clock.
   事故发生在六点钟。

hap.pen

v.intr.（不及物动词）
hap.pened,hap.pen.ing,hap.pens

To come to pass.
发生
To come into being.
出现
To take place or occur by chance.
偶然发生或出现
To come upon something by chance.
偶然遇到
To come or go casually; make an appearance.
偶然地来或去；露面

来源：
Middle English happenen
中古英语 happenen
from hap [chance] * see hap
源自 hap [碰巧] *参见 hap

<参考词汇><同义词>happen,befall,betide,chance,occurThe central meaning shared by these verbs is .to come about.:
这些动词所共有的中心意思是.发生.：
例句：
What would happen if you said noô
如果你拒绝的话，那么将会发生什么呢？

例句：
Who can predict the misery that may befall humankindô
谁又能够预测可能降临到人类头上的灾难呢？

例句：
Woe betide the poor soldier.
不幸降临于可怜的士兵身上。

例句：
It chanced that we succeeded.
我们侥幸取得了胜利。

例句：
The accident occurred recently.
这件事故就发生在最近。