Did Not Understood Or Understand?

Did Not Understood Or Understand? Did not understood or understand? 1 Answers. ”I didn’t understand. ” Since ‘did’ is the past tense of the auxiliary ‘do’, we can not have ‘understand’ in the past tense and therefore ‘understood’ is not permissible. Using both ‘did’ and ‘understood’ in a simple sentence like here is grammatically incorrect.