如果说keep sb away from doing sth 是阻止某人做某事,那么keep sb fron doing sth 应该是不阻止,即保持某人做某事,事实不是这样。
i prevent him from cutting tree.是我阻止他,他原先来自砍树这个状态
i keep就是保持,也就是不阻止,可还是说是阻止。