One of the most important rules to learn in English is that each tense takes an auxiliary verb. The auxiliary verb is conjugated while the main verb comes in either the base form (simple tenses), the 'ing' form (continuous tenses) or the participle form (perfect tenses). Here are some examples, auxiliary verbs are in italics while the main verbs are bolded:
She has visited Paris twice.
Do you live in Seattle?
Tom isn't coming to the meeting next week.
One of the most important exceptions to this pattern in English is when using positive sentences in the present simple and past simple.
Tom doesn't live in New York.
Do they enjoy coffee?
I play golf on Saturdays. - Notice there is no 'do' in this positive sentence
Frank didn't feel well last week.
Did we finish the project yesterday?
Alison went to the party last night. - Notice there is no 'did' in this positive sentence
Exceptions to the Rule #1
So far, so good you might be saying, but ... I've heard native English speakers say: 'Yes, I do live in Seattle.' Isn't that incorrect?! Unfortunately, the answer is it's correct in certain circumstances.
Sometimes, people might say saying that is contrary to the our knowledge. In this case, we correct the statement by stressing the auxiliary verb. For example,
- Sharon hasn't played the piano today.
- Yes, she has played the piano today. She practiced earlier this morning.
- Peter isn't coming tomorrow.
- No, that's not right. Peter is coming tomorrow. He called me earlier to tell me that he had changed his plans.
In the case of the present simple and past simple we add the auxiliary verb (do or did) when correcting incorrect information in this manner as an exception to the rule.
- Susan doesn't enjoy playing golf.
- That's not true. Susan does enjoy playing golf. We played last week!
- William didn't attend the meeting last month.
- No, he did attend the meeting. I went to his presentation!
Exception to the Rule #2
We also use 'do' and 'did' as an exception to the rule to stress a point we are making in the same manner. This form is often used to express something that we especially enjoy doing. Here are some examples:
I do enjoy drinking coffee in the morning!
She did value her time spent in Russia.