grammar - Omitting articles when contrasting people or things with "and"

There's a rule that says articles can be omitted when nouns referring to two contrasting people or things are joined by 'and'.

The independent allowances for husband and wife will both be
available.

...the natural relationship between father and son.

In a formal sense, the main difference between teacher and student is the amount of education.

...as the distinctions between employer and employee are

gradually eroded.

...with little gardens between river and road.

There was a pause, and doctor and patient looked steadily at each
other across the quiet room.

Does the same principle apply to nouns that by default have the definite article? If so, are the sentences below correct? Why is the definite article in sentence 3 omitted in the phrase "whereas for past tense"? Shouldn't it be "the past tense"? Is the definite article in "past tense" omitted because there's also an element of contrast?

1. The relation between the sexes has always found its cosmic expression
   in the relation between moon and sun. (I'm talking about the earth's moon and sun)




2. Even as the French king was hatching plans to destroy and annihilate a nascent coexistence between English language and
   English national identity, the supremacy of French culture was
   preserved by the language in which late medieval England conducted its
   official business. (Can the definite article in "English language" be omitted?)




3. For English, Huddleston and Pullum (2002: 143) point out that the difference between present perfect and past tense is that in
   the present perfect the primary focus is on the present moment,
   
   whereas for past tense it is on the past.