somethingstrange为啥放在后面

形容词修饰名词时经常放在名词前来修饰名词，例如:rainy day.但当被修饰的词为anything，something，nothing等不定代词时，形容词放在其后，例如:Something strange happened to him last Saturday.句意:上周星期六，奇怪的事发生在他身上了.