French Grammar: Partitive Articles

Definitive: A partitive article consists of the preposition de followed by a definite article (du, de la). It is frequently used before a singular noun that represents something that can be divided into smaller parts like liquids, wood, food, etc.

Je bois du vin rouge pour le dîner. Marie boit de la bière.
I drink red wine during dinner. Mary drinks beer.

Coupez nous du bois pour le feu.
Cut us some wood for the campfire.

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.
Partitive article vs Definite article
The partitive is usually used when discussing eating or drinking, because one normally only eats some butter, cheese, etc., not all of it. If you want to say that you eat all of something, use the definite article:
J'ai mangé du gâteau
I ate some cake (one piece).

J'ai mangé le gâteau
I ate the cake (the whole thing).
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 de la tarte
He ate some pie.

Il a préparé une tarte
He made a pie.
After adverbs of quantity, de is used instead of the partitive article.
Il y a beaucoup de thé
There is a lot of tea.

J'ai moins de glace que Carlos
I have less ice cream than Carlos.
In a negative construction, the partitive article changes to de, meaning any:
J'ai mangé de la soupe
Je n'ai pas mangé de soupe.

I ate some soup
I didn't eat any soup.