Learn Hardcore French: Ce pour quoi cette méthode est utile, c’est pour comprendre les petites nuances de la langue. - What this method is useful for is understanding the small nuances of the language.

pourquoi (one word) is an adverb meaning “why” (for asking questions):
- Pourquoi cette méthode est-elle utile ? = “Why is this method useful?”
pour quoi (two words) is préposition + relative/interrogative pronoun:
- pour = for
- quoi = what/which (after a preposition)

In this sentence, we’re not asking “why”; we’re saying “that for which…”, so it must be pour quoi (two words):

Ce pour quoi cette méthode est utile = “That for which this method is useful.”

What kind of structure is Ce pour quoi …, c’est …? Why this word order?

This is a type of cleft sentence (phrase clivée), used to add emphasis or highlight a specific part of the sentence.

Pattern:

Ce + relative clause + , c’est + [focused element]

Examples:

Ce que j’aime, c’est le chocolat. = “What I like is chocolate.”
Ce pour quoi cette méthode est utile, c’est pour comprendre…
= “What this method is useful for is (for) understanding…”

A non‑emphatic, “normal” version would simply be:

Cette méthode est utile pour comprendre les petites nuances de la langue.

The cleft form puts strong focus on the purpose of the method.

Why is there a c’est after the comma? Could we leave it out?

In this cleft structure, c’est is required. It introduces the element being highlighted.

Structure:

Ce pour quoi cette méthode est utile, c’est [pour comprendre les petites nuances de la langue].

If you remove c’est, you break the pattern and the sentence becomes ungrammatical:

✗ Ce pour quoi cette méthode est utile, pour comprendre les petites nuances… (wrong in standard French)

If you don’t want c’est, you must change the structure entirely:

Cette méthode est utile pour comprendre les petites nuances de la langue.

Why is pour repeated? Ce pour quoi … c’est pour comprendre… Isn’t that redundant?

It looks redundant in English, but in French the two pour have different roles:

Ce pour quoi cette méthode est utile
- pour belongs to être utile pour + quelque chose
- “what this method is useful for…”
c’est pour comprendre les petites nuances…
- pour + infinitif expresses purpose (“in order to”)
- “it’s for understanding the small nuances…”

So grammatically it’s:

“That for which this method is useful is (for) understanding…”

It’s acceptable and idiomatic.
You can streamline it to avoid the double pour:

Cette méthode est utile pour comprendre les petites nuances de la langue.
This is simpler and very natural, especially in speech.

Why utile and not utilisée here? What’s the difference?

utile is an adjective meaning “useful.”
- cette méthode est utile = “this method is useful.”
utilisée is the past participle of utiliser (“to use”), used in passive forms:
- cette méthode est utilisée = “this method is used.”

In the sentence, we want to say what the method is useful for, not that it is used:

cette méthode est utile (pour…) = “this method is useful (for…)”

So utile is correct. utilisée would change the meaning.

Could we say Cette méthode est utile pour comprendre les petites nuances de la langue instead? What’s the difference in meaning?

Yes, and that version is actually more common and more natural in everyday French:

Cette méthode est utile pour comprendre les petites nuances de la langue.

Difference:

Original (Ce pour quoi…, c’est…):
- More emphatic.
- Highlights the purpose as the key information.
- Slightly more formal / written style.
Simpler version (Cette méthode est utile pour…):
- Neutral statement.
- Very natural in speech and writing.

Meaning is essentially the same; only the focus and style change.

Could we say Ce à quoi cette méthode est utile instead of Ce pour quoi cette méthode est utile?

You can see both, but there is a nuance in how être utile is constructed:

être utile à quelqu’un / à quelque chose = to be useful to someone/something
- Cette méthode est utile aux étudiants. = “This method is useful to students.”
- → relative form: Ce à quoi cette méthode est utile… (“That to which this method is useful…”)
être utile pour + infinitif = to be useful for doing something
- Cette méthode est utile pour comprendre. = “This method is useful for understanding.”
- → relative form: Ce pour quoi cette méthode est utile… (“That for which this method is useful…”)

In your sentence, the focus is on an action (comprendre), so pour + infinitive is the natural choice:

Ce pour quoi cette méthode est utile, c’est pour comprendre…

Ce à quoi cette méthode est utile… suggests “what it is useful to” (often a person/thing), not “what it is useful for doing.”

Why is it les petites nuances de la langue and not something like des petites nuances or nuances de langue?

A few points:

les petites nuances
- les = “the” → we’re talking about all those small nuances in general, not just some:
  - les petites nuances = “the small nuances.”
de la langue
- de la langue = “of the language” (in general, an abstract sense).
- It’s like saying: “the small nuances of (the) language.”
- You could specify: de la langue française = “of the French language.”

Alternatives change the nuance:

des petites nuances de la langue = some small nuances of the language (not all)
nuances de langue would need a determiner (e.g. des nuances de langue), and it tends to sound more technical (as in discussions of stylistics or linguistics).

Where else could petites go in this noun phrase? Why is it before nuances?

In French, most adjectives come after the noun, but some common, short adjectives (including petit / grande / beau / bon / mauvais / jeune / vieux / nouveau) usually come before the noun.

So:

les petites nuances is the normal order.

You could say les nuances petites only in special, emphatic, or poetic contexts, and it would sound odd or marked in everyday French. Here, les petites nuances is the natural form.