praise sb  for doing sth

strike down sth for sth

for doing sth 为原因状语。praise的语义决定了动名词的逻辑主语是宾语而不是句子的主语。传统语法将for doing sth分析为原因状语。现代语法将这个for doing sth分析为动词的补足语，即使动词语义完整不可缺少的结构。正因为它是动词的补足语，不是状语，因此不可以移至句首。例如：

But the law was later struck down by the courts for violating free speech.

But for violating free speech the law was later struck down by the courts. (误）

We praised her for winning the competition.

For winning the competition we praised her. （误）

如果我们将for改为because of, 则为原因状语，而不再是动词的补足语。此时动名词的逻辑主语如果不是句子的主语，就要用动名词复合结构。

But the law was later struck down by the courts because of it(s) violating free speech.

But because of it(s) violatinig free speech, the law was later struck down by the courts.

We praised her because of her winning the competition.

Because of her winning the competition, we praised her.

同理，stop/prevent sb from doing sth 这样的结构中，from介词短语并不是状语，而是动词的补足语，不可以移至句首。动名词的逻辑主语是宾语而不是句子的主语。

如果能够区分谓语动词的补足语和状语，那么就可以说介词+动名词作状语（即不是动词的补足语），动名词的逻辑主语必须是句子的主语，否则动名词就要用复合结构，表示出自己的逻辑主语。