祈使句的結構是:Do sth.(否定式:Don't do sth.)
這個結構是屬於句子的範疇。
eg. Keep quiet!
Stop talking!
Don't talk with your mouth full!
Don't put your book here!
不定式的結構是:to do sth,這個結構可以充當主語,賓語,賓語補足語,定語,狀語等等。
這個結構只是充當句子的成分。
eg. To see is to believe. (做主語)
I find it useful to learn English well.(不定式做賓語)
He asked me to talk about English study. (不定式做賓語補足語)
I have nothing to say on this question.(不定式做定語)
He stopped to have a rest.(不定式做狀語