For example the sentence "I eat pizza" (without "do") is syntactically equivalent to "I do eat pizza" (with "do").
|Type||Without do||With do||Notes|
|Present simple||I/you/we/they eat pizza||I/you/we/they do eat pizza|
|3rd person singular, present tense||He/she eats pizza||He/she does eat pizza||Marked with third person -s|
|past tense||He/she ate pizza||He/she did eat pizza||Marked for past tense|
|Wh- question (present tense)||Who writes those books?||Who does write those books?||We can only do this with wh- questions with who, what, which and whose.|
|Wh- question (past tense)||Who wrote those books?||Who did write those books?|
- There may be a more formal name for this