They mean different things. The first one, "romantic" is a noun. In the second sentence, "romantic" is an adjective. The first sentence has similar grammar rules to the sentence "I am a Protestant". In the example sentence, the speaker is a member of the Protestant Church. The way that "I am a romantic" may work is that the speaker is a type of person, place, or thing, known as a romantic, like h

"I am a romantic."

Can I write in the same fashion "they are a romantic." ? If I can write then Why should I use "a" to show Romantic as noun though here plural They have used? But if I can't write then please correct "they are a romantic." in which I want to use "Romantic" as a noun BUT not as an adjective.

AnonymousThe first one, "romantic" is a noun

deba672Can I write in the same fashion "they are a romantic." ?

No. They are romantics.

"I am a doctor."
"They are a doctors."
Then can't I skip "a" in the previous sentence. Is it mandatory? then why? and what about "They are (blank) Doctors"?

Because you are speaking in plural.
DoctorS is plural ergo there is no need for the 'a'.
Doctor is singular.
The English language is tricky like this

AnonymousDoctor is singular

That is what my question is. As Doctor is singular why we need "a" there.

In English concrete singular nouns require an article such as "a" or "the".

You need "a doctor" to distinguish it from "the doctor". This makes a difference in English.

CJ

CalifJim to distinguish it from "the doctor"

What do you mean?

deba672What do you mean?

I mean you can't just use "doctor". You need "a doctor" or "the doctor".

If you write "a doctor", it means that you don't mean "the doctor".
If you write "the doctor", it means that you don't mean "a doctor".

"the doctor" is the doctor you are talking about in your conversation.
"a doctor" is any doctor at al

Both are correct and here's why: they mean two different things. "I am a romantic" is referring to a noun ("a romantic"). Just like a person can be "a doctor" or "a scallywag," he/she can be "a romantic." It is a label that is attached to a person based on how he/she is seen by others (or by him/herself).
"I am romantic," on the other hand, is using the word not as a noun, but as an adjective