(1)take place 一般指非偶然性事件的“发生”,即这种事件的发生一定有某种原因或事先的安排,例如: Great changes have taken place in our hometown during the past ten years. The Olympic Games of 2008 has taken place in Beijing.
(2)happen一般用于偶然或突发性事件,例如: What happened to you? (一般不说:What did you happen?) Maybe something unexpected happened. I happened to see him on my way home. = It happened that I saw him on my way home.
Great changes have taken place in the last three years. 过去的3年里发生了很大的变化。 happen有时指没有思想准备的事或者不清楚会发生的事(如:what happened?) take place 在这里指顺利的有计划的发生(如:the annual celebration took place yesterday)