Learn French: Le client n'achète ni la cravate ni la veste. - The customer buys neither the tie nor the jacket.

When using the multiple negation ne... ni... ni... (neither... nor...), the word pas is dropped completely. The ni... ni... replaces it to complete the negative meaning.

Normally, negative sentences change the article to de. Why is it still la cravate and la veste here?

That rule only applies to indefinite (un, une, des) and partitive (du, de la) articles. Definite articles like le, la, and les never change to de in the negative. Because we are talking about specific items (the tie, the jacket), the la stays exactly as it is.

Where does the ne go when listing multiple things with ni?

Just like standard negation, the ne (or n' before a vowel, as in n'achète) goes directly in front of the conjugated verb. Then, you place ni directly in front of each noun you are excluding.

Why does achète have a grave accent (è) when the infinitive acheter doesn't?

Acheter (to buy) is a stem-changing verb. In the present tense, when the stress falls on that syllable (which happens for je, tu, il/elle/on, and ils/elles), the silent e changes to è so it can be pronounced clearly. It's a great pattern to remember as you build your vocabulary!