Du gâteau?
The partitive articles in French correspond to « some » or « any » in English. There are four forms of the French partitive article:
  1. du masculine singular
  2. de la feminine singular
  3. de l’ m or f in front of a vowel or h muet
  4. des m or f plural

The form of the partitive article to use depends on three things: the noun’s number, gender, and first letter:

  • If the noun is plural, use des
  • If it’s singular starting with a vowel or h muet, use de l’
  • If it’s a singular noun and starts with a consonant or h aspiré, use du for a masculine noun and de la for a feminine noun
Meaning and usage of the French partitive article The partitive article indicates an unknown quantity of something, usually food or drink. It is often omitted in English.Avez-vous bu du thé ?
Did you drink (some) tea?J’ai mangé de la salade hier.
I ate salad yesterday.Nous allons prendre de la glace.
We’re going to have some ice cream.

EXPRESSIONS of QUANTITY: After adverbs of quantity, use de instead of the partitive article.

Il y a beaucoup de thé.
There is a lot of tea.

J’ai moins de glace que Thierry.
I have less ice cream than Thierry.

In a negative construction, the partitive article changes to de, meaning « (not) any »:

J’ai mangé de la soupe. > Je n’ai pas mangé de soupe.
I ate some soup. > I didn’t eat any soup.

The French articles may seem similar at times, but they are not interchangeable. This page will help you understand when and why to use each one.
 Definite article
The definite article can talk about a specific item or something in general.J’ai mangé le gâteau.
I ate the cake (the whole thing, or the specific cake that we were just talking about).

J’aime les films.
I like movies (in general) or I like the movies (that we just saw).

Indefinite article
The indefinite article talks about one of something, and is the easiest of the French articles. I can almost guarantee that if what you want to say requires « a, » « an, » or « one » in English – unless you’re talking about someone’s profession – you need the indefinite article.

J’ai mangé un gâteau.
I ate one cake (there were five, and I ate one of them).

Je veux voir un film.
I want to see a movie.

Partitive article
The partitive is usually used when discussing eating or drinking, because one normally only eats some butter, cheese, etc., not all of it.

J’ai mangé du gâteau.
I ate some cake (one slice, or a few bites).

Je cherche de l’eau.
I’m looking for some water.

Partitive article vs Indefinite article
The partitive indicates that the quantity is unknown or uncountable. When the quantity is known/countable, use the indefinite article (or a number):

Il a mangé du gâteau.
He ate some cake.

Il a mangé un gâteau.
He ate a cake.

(explanation & examples from http://www.aboutfrench.com)
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