“凭空杜撰”英语怎么说？

to work/contrive when shut oneself in

to work behind closed doors

to work behind closed doors;

to do sth blindly;

to divoice oneself from reality when carrying out a project;

to do sth without any knowledge of the actual process;

除了您举的曲译外，还有下面两种表达：

1，To work behind closed doors;

2, To divorce oneself from the masses and from reality and act blindly.