Learn Hardcore French: Au café, il trouve impoli de parler trop fort, et il aime les clients polis. - At the café, he finds it impolite to speak too loudly, and he likes polite customers.

Au café: more general, “at the café” as a location or setting.
- Example: Au café, on boit souvent un expresso. (At the café, people often drink an espresso.)
Dans le café: more specific, physically inside the building.
- Example: Il y a beaucoup de monde dans le café. (There are many people in the café.)

In your sentence, Au café sets the general scene: in that environment, he considers certain behavior impolite and likes polite customers.

Why does the sentence say il trouve impoli de parler trop fort instead of something like il pense que parler trop fort est impoli?

Both structures are correct, but they are built differently.

il trouve impoli de parler trop fort
- Structure: trouver + adjective + de + infinitive
- Meaning: “he finds it impolite / he considers it impolite to speak too loudly.”
- This is a very natural, compact way in French to express a judgment about an action.
il pense que parler trop fort est impoli
- Structure: penser que + clause
- Also correct, but a bit heavier stylistically.
- More literally: “he thinks that speaking too loudly is impolite.”

In everyday French, trouver + adjective + de + infinitive is very common for opinions about actions:

Je trouve dangereux de conduire si vite. (I find it dangerous to drive so fast.)
Nous trouvons normal de payer. (We find it normal to pay.)

So your original version is idiomatic and natural.

Why is there a de before parler: il trouve impoli de parler trop fort? Why not just il trouve impoli parler trop fort or à parler?

In French, a common pattern is:

trouver + adjective + de + infinitive

The de introduces the infinitive clause (the action being judged).

Examples of the same pattern:

Je trouve utile de réviser tous les jours.
Elle trouve bizarre de manger si tard.

You generally do not say:

✗ il trouve impoli parler trop fort
✗ il trouve impoli à parler trop fort

So de parler is required by the grammar of this construction.

Why is impoli in the masculine singular form here, and what is it agreeing with?

In il trouve impoli de parler trop fort, the adjective impoli is masculine singular because it’s part of a neutral, general structure.

You can think of an underlying structure like:

Il trouve qu’il est impoli de parler trop fort.
(“He finds that it is impolite to speak too loudly.”)

That il is a kind of “dummy” or neutral il, which is always masculine singular. So impoli also appears in masculine singular.

Contrast with other cases where the adjective clearly agrees with a noun:

Cette remarque est impolie. (feminine singular, because remarque is feminine)
Ces remarques sont impolies. (feminine plural)

Here, the thing judged is the general action parler trop fort, not a specific noun with gender. French falls back on a neutral-looking structure using masculine singular.

Why is there no article before impoli? Why don’t we see something like un impoli?

In this sentence, impoli is an adjective, not a noun.

il trouve impoli de parler trop fort
→ impoli = adjective meaning “impolite”, describing the action.

Adjectives do not take articles when they directly follow verbs like être, sembler, devenir, rester, trouver as adjectives:

Il est impoli. (He is impolite.)
Je la trouve intelligente. (I find her intelligent.)

You would only see something like un impoli if impoli is used as a noun:

C’est un impoli. (He’s a rude person / this is a rude guy.)

That is a different use, talking about a person as “an impolite one”, not about an action as “impolite”.

What is the difference between parler trop fort and parler très fort?

trop = “too (much)”, so parler trop fort means to speak too loudly.
It includes a negative judgement (excess).
très = “very”, so parler très fort means to speak very loudly, without necessarily saying it’s “too much” or wrong.

In your sentence, he finds it impolite, so trop is appropriate:

Il trouve impoli de parler trop fort.
→ He thinks people are speaking louder than they should.

If you said:

Il parle très fort.
→ He speaks very loudly (neutral description; might or might not be a problem).

Why is it les clients polis and not des clients polis?

French uses les (the) for general categories much more than English does.

Il aime les clients polis.
- Literally: “He likes the polite customers.”
- Actually means: “He likes polite customers (in general, as a group/type).”

If you said:

Il aime des clients polis.
- This sounds odd or very specific, as if talking about some particular polite customers he knows or has, and even then it is not very natural with aimer.

So:

les clients polis → the category “polite customers” in general.
English often drops the article in such generalizations, but French usually keeps les.

Why is the adjective polis placed after clients? In English we say “polite customers,” with the adjective before.

In French, most adjectives normally come after the noun:

un homme poli (a polite man)
des clients polis (polite customers)

Only certain common adjectives (often short and very frequent) come before the noun: e.g. petit, grand, beau, vieux, nouveau, bon, mauvais, jeune etc.

Examples:

un petit café
un bon client
un vieux monsieur

But adjectives like poli, intelligent, intéressant, important, français, etc. usually go after the noun:

un client poli
une femme intelligente
un livre intéressant

So les clients polis is the standard word order.

Why do clients and polis have an s at the end, and how is it pronounced?

Both clients and polis are in the plural:

client → clients (add -s)
poli → polis (add -s)

In French spelling, -s usually marks the plural, but it is often silent in pronunciation.

Pronunciation:

clients → /kli.jɑ̃/ (the final -s is silent)
polis → /pɔ.li/ or /po.li/ depending on accent (final -s silent)

The plural is mainly heard through:

the article: le client vs les clients
liaison in some contexts (e.g. les amis → /lez‿ami/)

In les clients polis, there is no required liaison before clients, so the s is not heard; it just shows plurality in writing and agreement.

Who does il refer to in this sentence? Could it mean “one” like English “one finds it impolite…”?

Grammatically, il is third person singular and usually means he.

In a real context, il would refer to a specific man already mentioned:

Paul travaille dans un bar. Au café, il trouve impoli de parler trop fort…
(Paul works in a bar. At the café, he finds it impolite to speak too loudly…)

If the meaning were truly general (“people in general find it impolite…”), French more naturally uses on:

Au café, on trouve impoli de parler trop fort.
→ “At the café, people find it impolite to speak too loudly.”

So in isolation, il is best understood as he, not the impersonal “one”.

Could we also say Au café, c’est impoli de parler trop fort or Au café, il est impoli de parler trop fort? Are those correct?

Yes, both are grammatically correct and natural, with slightly different flavors:

Au café, c’est impoli de parler trop fort.
- Very common in spoken French.
- Neutral: “At the café, it’s impolite to speak too loudly.”
Au café, il est impoli de parler trop fort.
- A bit more formal or written.
- Same meaning: “At the café, it is impolite to speak too loudly.”
Au café, il trouve impoli de parler trop fort.
- Adds a subject with an opinion: he finds it impolite.

So:

With c’est or il est, you state a general rule.
With il trouve, you emphasize this particular person’s opinion.

Is there a difference between les clients polis and les clients qui sont polis?

Both are grammatically correct and close in meaning, but:

les clients polis
- More compact and natural.
- Simple adjective phrase: “polite customers.”
les clients qui sont polis
- Literally: “the customers who are polite.”
- Often used when you want extra emphasis or add more information:
  - les clients qui sont polis et respectueux
  - les clients qui sont polis avec le personnel

In your sentence, les clients polis is perfectly natural and preferred.