Learn Hardcore French: Bien sûr, Paul garde du beurre au frigo pour le petit-déjeuner. - Of course, Paul keeps butter in the fridge for breakfast.

Feminine mass noun: de la confiture (some jam)
Before a vowel or mute h: de l’eau (some water)
Plural countables: des œufs (some eggs) Note: after most negatives and quantity expressions, the partitive becomes de (see below).

Could I say le beurre or son beurre instead of du beurre?

Yes, but the meaning changes:

le beurre = a specific, known butter (or “butter” in general as a category)
son beurre = his butter (the butter that belongs to Paul)
du beurre = an unspecified quantity of butter Choose based on how specific you want to be.

Is au frigo really “in the fridge”? Why not dans le frigo?

Both are fine:

au frigo (à + le) is a very common idiomatic way to mean “in the fridge” with verbs like mettre/garder/laisser. It’s natural in speech.
dans le frigo is the literal “in the fridge.” Also perfectly correct. Similar idioms: au four, au micro-ondes, au placard, à la poubelle.

Is frigo informal? Should I prefer réfrigérateur?

Frigo is widely used and perfectly fine in everyday speech and most writing. Réfrigérateur is more formal/technical. You might prefer réfrigérateur in formal writing or instructions.

Why is it pour le petit-déjeuner rather than au petit-déjeuner?

pour le petit-déjeuner = “for breakfast” in the sense of purpose/intent (why he keeps it).
au petit-déjeuner = “at/for breakfast” in the sense of the mealtime context (what one eats/drinks then). Examples:
Je garde du pain pour le dîner. (purpose)
Je bois du café au petit-déjeuner. (mealtime context)

Does petit-déjeuner need a hyphen? And is it capitalized?

Spelling: The 1990 reform recommends petit-déjeuner (hyphen). The older petit déjeuner (two words) is still accepted. You’ll see both.
Capitalization: In French, meal names are not capitalized unless they start the sentence: le petit-déjeuner.

What does Bien sûr add here? Do I need the comma? Can it be ironic?

Bien sûr means “of course,” adding confirmation or obviousness. The comma sets it off as a parenthetical, which is standard.
It can be neutral, warm, or even ironic/sardonic depending on tone.
Mind the accent: sûr (sure) vs sur (on). They’re different words.

Why is garde in the present tense? Does it imply a habit?

Yes. French present tense commonly expresses habits and general truths. Paul garde… = “Paul keeps…” as a habitual practice. If you needed a current ongoing action, you could say Paul est en train de garder…, but that’s rare here.

Could I use a different verb instead of garder?

Yes, with nuances:

mettre au frigo = to put in the fridge (the act of placing)
laisser au frigo = to leave in the fridge
conserver au réfrigérateur = to preserve/store (more formal/technical)
ranger au frigo = to put away in the fridge
stocker au frigo = to stock/store (practical/logistical)

What are the genders of beurre, frigo, and petit-déjeuner?

All three are masculine:

le beurre → du beurre
le frigo → au frigo
le petit-déjeuner → pour le petit-déjeuner

How do du and au form? Why can’t I write de le or à le?

French contracts:

de + le → du; de + les → des
à + le → au; à + les → aux You can’t write de le or à le; you must use the contracted forms. Before vowels/mute h: de l’, à l’ (no contraction).

How would I replace du beurre with a pronoun?

Use en (it replaces “de + noun”):

Bien sûr, Paul en garde au frigo pour le petit-déjeuner. If you also replace “au frigo” with y:
Bien sûr, il y en garde pour le petit-déjeuner. Pronoun order reminder: me/te/se/nous/vous + le/la/les + lui/leur + y
- en.

How do I say it in the negative?

General negation with a mass noun: Bien sûr, Paul ne garde pas de beurre au frigo pour le petit-déjeuner. (partitive → de)
If it’s specific butter: … ne garde pas le beurre … (you keep the definite article)

Can I move parts of the sentence around?

Yes, French allows some flexibility for emphasis:

Pour le petit-déjeuner, Paul garde du beurre au frigo. (fronts purpose)
Au frigo, Paul garde du beurre pour le petit-déjeuner. (fronts place)
Paul garde au frigo du beurre pour le petit-déjeuner. (also possible) Keep pronouns before the verb; avoid stacking too many long phrases at the end.

Any pronunciation tips for tricky bits?

Bien sûr: nasal vowel in bien; sûr has the French u sound; the r is uvular.
du: “dy.”
beurre: the vowel is like the “eu” in French “peur”; final r is uvular.
frigo: stress typically at the end; hard g.
petit-déjeuner: the t in petit is usually heard here because of the compound; think “p(uh)-TEE day-zhuh-nay.” Avoid pronouncing every letter; French often drops final consonants unless liaison or compounds require them.

Are there regional differences for petit-déjeuner?

Yes. In France, le petit-déjeuner = breakfast, le déjeuner = lunch, le dîner = dinner. In much of Québec/Belgium, le déjeuner often means breakfast, le dîner lunch, le souper dinner. So petit-déjeuner is standard in France; in Québec, people more often say déjeuner for breakfast.