Absence of the articles in set expressions

at dinner (breakfast, etc.) at first notice at first sight at night at table at war	in search of in spite of
by airmail by letter by telegram by air by car by land by plane by sea by ship (boat) by train by tram by tube by water	out of date out of order out of place out of sight
arm in arm day after day day by day hand in hand night after night night by night
a kind of a sort of	place, book, task, etc.
by accident by chance by mistake by name by sight	on account of on condition that
to be in to go to	bed
from beginning to end from day to day from east to west from head to foot from morning to (till) night from side to side   in debt in demand in secret in sight in time	to be at to go to to come to to come from to leave	school, college, (the) university
to be at to leave to take to	hospital
to be at to go to	sea
in addition to in (on) behalf of in care of in case of in charge of in reference to	to be in to go to	church
to be at to put to	prison
to be in to be out of to go to	town
to ask (for) permission to catch (lose) sight of   to give offence (permission) to give way to   to keep house (to do housework) to keep time	to lose touch with to lose track of to make fun of to make use of to pay attention to to set fire to to shake hands with to take care of to take notice of

In these set expressions nouns combine with prepositions or verbs and acquire a new shade of meaning, expressing an adverbial relation, a state or a process. Concrete count nouns lose their nominal meaning. Thus He isin bed may mean He is ill, or He is asleep, or He is not up. But we say: There were no chairs enough and we sat onthe bed.

My brother goesto school (college) means He learns there. However, if we mean the building or the institution, we use an article according to the general rules, as in: We shall meet atthe school. The school isn't far from our home. Ours is a verygood school. Parents are regularly invited tothe school.

The noun town without an article means the nearest big centre of population as contrasted to the country or a smaller town, it may also denote the central part of a big town, as opposed to its suburbs.

To be at sea may mean "far away from the land" or (figuratively) "to feel puzzled"; to go to sea is "to become a sailor". But we say: The swimmer jumped into the sea. We lived near the sea, etc.

No article is used as a rule when two notions, very closely related, are mentioned, as in:

They looked like mother and daughter.

We are no longer boy and girl.

It’s no use interfering into a quarrel between husband and wife.