Learn Hardcore French: Paul ne mange ni viande ni poisson.

Ni ... ni is a correlative negation meaning neither ... nor. It replaces the usual ne ... pas. You keep ne before the verb, but you do not add pas: Paul ne mange ni viande ni poisson.

Why are there no articles like de la viande or du poisson?

With ni ... ni, French generally drops the indefinite/partitive articles when listing generic items: ni viande ni poisson. If you refer to specific, identified items, you keep the definite articles and repeat them: Il n’aime ni la viande ni le poisson.

Can I say Paul ne mange pas de viande ni de poisson?

It’s acceptable and common in speech (an asymmetric pattern: pas ... ni ...). In careful, balanced style, Paul ne mange ni viande ni poisson is preferred, especially in writing.

Should I ever keep the articles with ni ... ni?

For generic, unspecified items: drop them (preferred): ni viande ni poisson.
For specific or previously mentioned items: keep the definite articles and repeat them: ni la viande ni le poisson que tu as préparés.
Do not keep partitive articles in the generic case: avoid ni du poisson here.

How do I say “either meat or fish” (the positive alternative)?

Use ou ... ou: Paul mangera de la viande ou du poisson.

Where do the negatives go in compound tenses?

Place ne before the auxiliary; ni ... ni stays before the coordinated items:

Paul n’a mangé ni viande ni poisson.
Paul ne mangera ni viande ni poisson.

Can ni ... ni link things other than nouns?

Yes:

Adjectives: Il n’est ni riche ni pauvre.
Verbs: Il ne boit ni ne fume. (repeating ne before the second verb is standard)
Phrases: Il ne mange ni chez lui ni au restaurant.

Is the ne obligatory? I often hear it dropped.

In casual speech, many speakers drop ne: Paul mange ni viande ni poisson. In writing and formal contexts, keep ne.

What changes if I’m talking about likes/dislikes rather than consuming?

With verbs of preference (e.g., aimer, détester), use definite articles, even in negation: Il n’aime ni la viande ni le poisson.

How do I add adjectives like “red meat” or “raw fish”?

Attach the adjectives, still without articles in the generic case: Il ne mange ni viande rouge ni poisson cru. If referring to specific items, use definite articles: ni la viande rouge ni le poisson cru.

Do I need to repeat ni before each item?

Yes. Repeat ni before each coordinated element: ni viande ni poisson ni œufs (for three items). Don’t mix ni with ou in the same list.

Can I replace the nouns with a pronoun?

Use en with a clarifier:

Il n’en mange ni l’un ni l’autre. (neither of the two)
Il n’en mange aucun des deux. Avoid the incomplete Il n’en mange ni.

How do I say “Paul doesn’t either” after a negative statement?

Use non plus:

Marie ne mange pas de viande. Paul non plus.
After a ni ... ni sentence: Paul ne mange ni viande ni poisson. Marie non plus.

Any pronunciation tips (especially poisson)?

Paul ≈ “pohl”
ne often reduced to a very light sound, or dropped in speech
mange ≈ “mahnzh” (soft g like the s in “measure”)
viande ≈ “vyahnd” (nasal vowel)
poisson ≈ “pwah-sohn” (final nasal vowel). Don’t confuse with poison ≈ “pwah-zohn” (means “poison”).

Why is there no de before viande/poisson, but I do see de with ni in other sentences?

Here, de would be a partitive article, which is normally dropped with ni ... ni in the generic case. However, keep a true preposition required by the verb:

Il n’a parlé ni de toi ni de moi. (the verb is parler de) That de is a preposition, not a partitive article.

Any spelling/grammar pitfalls with mange?

mange is the 3rd person singular of manger; the final -e is silent.
To keep the soft g before -ons, it’s nous mangeons (with an extra e).