Formal legal and economic writing leans heavily on complex sentences built from relative clauses, and getting the relative pronoun right — dont, lequel/laquelle, auquel, duquel, and their plural forms — is one of the clearest markers of command over written register at B2 and beyond. The core principle: French chooses its relative pronoun based on which preposition the verb or noun inside the relative clause requires, not on the antecedent's role in English (where 'whose', 'which', and 'that' get stretched to cover almost everything).
Dont is the pronoun for any relative clause where the missing element is introduced by de: it replaces de qui, duquel, or de laquelle whenever a simple de-relationship is involved, and it covers three distinct English translations depending on context — 'whose' for possession ('l'entreprise dont le PDG a démissionné', the company whose CEO resigned), 'of which/about which' for verbs and expressions built with de ('le dossier dont nous avons discuté', the file we discussed — from discuter de), and simply 'that... of' for nouns paired with de ('un projet dont l'ampleur surprend', a project whose scale is surprising — from l'ampleur de). Because dont already contains de, you must never add a second de anywhere else in the clause — 'le livre dont j'ai besoin de' is a doubling error; dont alone does the whole job of avoir besoin de.
When there's no explicit antecedent noun to attach dont to, French uses ce dont: 'Voici ce dont nous avons besoin pour conclure l'accord' (Here is what we need to close the deal). This parallels ce que/ce qui from indirect questions, but specifically for the de-relationship.
For every preposition other than de, French uses the lequel family instead, which agrees in gender and number with its antecedent and contracts with à and de exactly like the definite article does: à + lequel → auquel, à + lesquels → auxquels, à + lesquelles → auxquelles. 'Le tribunal auquel l'affaire a été renvoyée' (the court to which the case was referred) uses auquel because renvoyer is followed by à. With compound prepositions that happen to end in de (à côté de, au sujet de, en raison de, à l'égard de), dont is not used — instead you need duquel/de laquelle/desquels, because dont can only replace a bare, simple de, not de as the tail end of a longer preposition: 'l'immeuble au sujet duquel le litige a éclaté' (the building the dispute arose about), never 'l'immeuble dont le litige a éclaté au sujet.' Choosing correctly between dont and duquel/de laquelle in these compound-preposition cases is exactly the kind of fine distinction that marks genuinely advanced written French.
Exemples
L'entreprise dont le chiffre d'affaires a doublé cherche de nouveaux investisseurs.
The company whose revenue has doubled is seeking new investors.
Dont expressing possession (le chiffre d'affaires de l'entreprise).
Voici les documents dont vous aurez besoin pour signer le contrat.
Here are the documents you will need to sign the contract.
Dont from 'avoir besoin de' — no extra 'de' allowed elsewhere in the clause.
C'est une clause dont la portée juridique reste incertaine.
It's a clause whose legal scope remains uncertain.
Voici ce dont il s'agit dans cette affaire.
Here is what this case is about.
Ce dont: no explicit antecedent, from 's'agir de'.
Le tribunal auquel l'affaire a été renvoyée rendra sa décision en mars.
The court to which the case was referred will rule in March.
Auquel = à + lequel.
La société avec laquelle nous négocions est cotée en bourse.
The company with which we are negotiating is publicly traded.
'Avec' + laquelle: not 'de', so dont is impossible here.
Les obligations auxquelles l'entreprise doit se conformer figurent dans l'annexe.
The obligations the company must comply with are listed in the appendix.
Auxquelles = à + lesquelles, plural feminine.
L'immeuble au sujet duquel le litige a éclaté appartient à la municipalité.
The building the dispute arose about belongs to the municipality.
Compound preposition ending in 'de': duquel required, not dont.
C'est précisément ce à quoi les actionnaires s'opposent.
That is precisely what the shareholders are opposed to.
Ce à quoi: no antecedent, from 's'opposer à'.
Erreurs fréquentes
- Adding a redundant second 'de' after dont, e.g. 'le contrat dont nous avons besoin de' instead of the correct 'le contrat dont nous avons besoin'.
- Using dont with a compound preposition ending in de (au sujet de, à côté de, en raison de) instead of switching to duquel/de laquelle/desquels.
- Using 'que' where dont is required, e.g. 'le projet que l'ampleur surprend' instead of 'le projet dont l'ampleur surprend'.
- Forgetting the à + lequel contraction and writing 'à lequel' or 'à laquelle' incorrectly instead of the contracted 'auquel'/'à laquelle' (laquelle does not contract, but auquel/auxquels/auxquelles do).
- Keeping the noun in its original position after dont instead of moving it immediately after dont, e.g. writing 'dont a démissionné le PDG' instead of 'dont le PDG a démissionné'.
Pourquoi ça trompe les anglophones
- English 'whose' and 'of which' flatten every de-relationship into one all-purpose word regardless of whether it marks possession, a verb's required preposition, or a noun complement, so English speakers have no instinct to check which underlying preposition (de vs à vs a compound) governs the clause.
- Because dont already absorbs the 'de', mentally translating word-for-word from an English 'of which I need' produces a doubled 'de' that isn't there in the English original at all.
- The lequel/laquelle/auquel/duquel family inflects for gender and number and contracts with à and de, a level of morphological agreement relative pronouns simply don't carry in English.