Dont in depth

Dont stands for de plus whatever follows it, so the test is to rebuild the clause: on parle de ce film, so c'est le film dont on parle. Parler de, avoir besoin de, se souvenir de, avoir peur de: every verb that takes de is a dont verb. If there is no de in the rebuilt sentence, dont is the wrong word.

English says the man whose son I know; French says l'homme dont je connais le fils. Two things to notice. After dont the word order is normally the plain subject, verb, object one, not inverted. And the possessed noun takes le, la or les, never son or sa, because dont has already said whose it is.

With no noun in front, dont becomes ce dont, just as que becomes ce que. The verb decides: je sais ce que tu veux (vouloir quelque chose), but je sais ce dont tu as besoin (avoir besoin de). After a number, dont gives the part of a total: trois enfants, dont deux filles.

Dont has to start its clause. When the de is the end of a longer preposition such as au bout de, près de or en face de, use duquel, de laquelle, desquels or desquelles instead: le pont au bout duquel se trouve l'église, never au bout dont.