1. He wants to be a singer in the future.
2. He was a lawyer in the past.
3. He is a doctor in the present.
4. He is a doctor at present.
5. He is a doctor at the moment.
6. He is a doctor currently.
7. He is a doctor now.
8. He is a doctor at the present.
(From #3 to #8, there are similar sentences. Are they grammatical? Which expressions should I use? Are they all the same in meaning?)
3-8 all mean the same thing, yes, and all are grammatically correct.
I wouldn't use #3. I'd use #8 with "at the present" or simply "at present" (#4) at the beginning of the sentence.
All of the sentences from #3 to #8 are grammatical and convey the same meaning. However, there are some differences in nuance and usage.
Sentence #3, "He is a doctor in the present," is grammatically correct but sounds a bit formal or stilted. It is less commonly used in everyday conversation.
Sentences #4 to #8, including "He is a doctor at present," "He is a doctor at the moment," "He is a doctor currently," "He is a doctor now," and "He is a doctor at the present," are more commonly used and have a more natural flow. They all mean that the individual is currently working as a doctor.
Out of these options, "He is a doctor now" is the most common and frequently used phrase to indicate the person's current profession.
Overall, you can use any of the sentences from #3 to #8 to convey that someone is currently working as a doctor. However, for everyday conversation, "He is a doctor now" is the most commonly used expression.