understand? understood?

[Polyester]

"Do you hear me? Don't kill people again. Understand?"
"Understood!"

Why people always say that past tense "understood" not "understand"?

Can someone explain to me,
thank a lot.

 

[probus]

To figure it out, you have to add the implicit tenses to the verbs. The tenses are omitted in your example because of extreme contraction in colloquial speech.

"Understand?" is a contraction of "Do you understand?"

The reply "Understood" is a contraction of "I have understood."

 

[Matthew Wai]

The reply "Understood" is a contraction of "I have understood."

Could it be a contraction of 'It is understood'?

 

[Polyester]

No. Incorrect.

 

[bhaisahab]

It could, Matthew. If the question is "Is it understood?"

 

[probus]

Could it be a contraction of 'It is understood'?

Sure. The point is that tense is needed in English. There may be more than one tense/grammatical form that is appropriate.