▲for generations（世世代代，祖祖辈辈）强调时间的长度，可以联想for days, for weeks, for months, for years, for centuries 等，这些表达均表示时间长度。注意体会：
We live here for generations. 我们祖祖辈辈都生活在这里。
My family has lived in this area for generations. 我的家好几代人都居住在这个地区。
The tradition has been passed down from father to son for generations. 这一传统由父传子，世代相传。
▲from generation to generation（一代一代地）强调时间的延续。注意体会：
Folk tales have been passed down from generation to generation. 民间故事代代相传。
His is a family trade, passed down from generation to generation. 他的生意是家族似的，是一代一代传下来的。
These jewels have been passed down in our family from generation to generation for hundreds of years. 这些珠宝在我们家代代相传已有好几百年的历史了。