My mother sighed melodiously, her way of warning present company that this could easily turn into an improvised lecture from the great man himself.
This is from "Call me by your name" by Andre Aciman.
How do you explain the absence of a definite article before present company? Is there a grammatical explanation or a rule?
In the fixed phrase "..., present company excepted" (used when making some criticism of a group that may include the people you are talking to) the work "company" is treated as uncountable, or rather it is an uncountable noun, singular in form, but referring to a plurality of people.
It is used as a fixed phrase, and you would not normally use "present company" in other grammatical contexts. Here it is used in reference to the idiom: "present company" is treated as a compound noun that means "those people who were around"
She warned those present that ...
She warned her guests ...
or allow context to fill in the object:
She warned that this could easily turn into a lecture
(Implicitly she is speaking to the people she is warning)
