do please

PEG(p.127)对这种用法do进行了详细的分析：

“do is placed before the imperative to make a request or invitation more persuasive:

Do come with us (more persuasive than Come with us).

Do work a little harder. Do help me, please.

It can similarly be used as an approving or encouraging affirmative answer to someone asking for approval of, or permission to do, some action: Shall I write to him? Yes, do or Do alone."

(“do 放在祈使句的前面,可使请求或邀请更有说服力:

同样，在有人请求同意或允许做某事时，do也可以用作赞同或鼓励的肯定回答语：

这就是说,PEG 的作者是肯定而明确地把此种用法的 do 划为加强祈使句语气的助动词的。由此可以证明,上面的 do 并不是替代词,见 $\mathrm{<span\; class="latin-run">d</span>}{\mathrm{<span\; class="latin-run">o</span>}}^4$do^{4} 。