'Do,' 'does,' and 'did' are auxiliary (helping) verbs that are used in questions, negatives, and emphatic statements. Here are the key distinctions:
1) Do vs. Does
a) Do is used with I, you, we, and they (plural or singular).
• I do my homework every day.
• They do not like the movie. (Negative)
b) Does is used with he, she, or it (singular).
• She does her work carefully.
• It does not make sense. (Negative)
Key rule: "Do" is for plural subjects or with "I/you," while "does" is for singular third-person subjects (he, she, it).
2) Did
a) Did is used for the past tense with all subjects (I, you, he, she, it, we, they).
• I did my homework yesterday.
• They did not attend the meeting. (Negative)
Key rule: "Did" is used for all subjects in the past tense, regardless of whether the subject is singular or plural.
3) Questions with Do, Does, and Did
a) Do is used for questions with I, you, we, and they.
• Do you like pizza?
• Do we have time for a break?
b) Does is used for questions with he, she, or it.
• Does she understand the problem?
• Does it work properly?
c) Did is used for questions in the past tense with all subjects.
• Did you enjoy the movie?
• Did they arrive on time?
4) Negative Sentences with Do, Does, and Did
a) For present tense, do and does are used in negative sentences:
• I do not (don't) like that book.
• He does not (doesn't) want to go.
b) For past tense, did is used in negative sentences:
• I did not (didn't) see her yesterday.
• They did not (didn't) play football last weekend.
5) Emphatic Statements
a) Do is used in the present tense to emphasize a statement:
• I do enjoy reading books. (Emphasizing enjoyment)
• They do understand the lesson. (Emphasizing understanding)
b) Did is used in the past tense for emphasis:
• She did help me with the project. (Emphasizing that she helped)
• I did call you earlier. (Emphasizing that the action happened)
Summary:
Do: Used for I, you, we, they (present tense, plural and singular).
Does: Used for he, she, it (present tense, singular).
Did: Used for all subjects in the past tense.