一定的人或事物certain

• 张某

  a certain person called Zhang

• 某城

  a particular city

• 某学校

  some school

• 解放军某部

  a certain unit of the PLA

• 由于某种原因

  because of certain reasons

不定的人或事物some

• 某天

  some day

• 某人

  someone

• 某地

  some place

• 他住在很远的某个地方。

  He lives in some faraway place.

• 为了商谈某事

  in order to discuss something

• 从某一时期起

  starting from a certain time period

用来代替自己的名字to refer to oneself

用来代替别人的名字to refer to someone else

• 请转告刘某，不要太骄傲自大。

  Please tell Liu that he shouldn't be so cocky.