Impersonal verbs (falloir, pleuvoir, s'agir)
Summary
Impersonal verbs exist only with the dummy subject il — never a real person or thing — and cover weather (il pleut), necessity (il faut), and a handful of fixed expressions (il s'agit de, il reste, il vaut mieux).
Explanation
Impersonal verbs are used only in the third-person singular with the dummy (non-referential) subject pronoun il, which points to no real person or thing — it simply fills the grammatical subject slot that French requires. Weather verbs are the clearest example: il pleut ('it's raining'), il neige ('it's snowing'), il gèle ('it's freezing'), il fait beau/froid/chaud/du vent ('it's nice/cold/hot/windy'). None of these can take a personal subject: there is no *je pleus.
The most important impersonal verb is falloir, expressing necessity. With a following infinitive or a noun it is invariable — il faut partir ('one must leave'), il faut du courage ('courage is needed') — and it never changes to agree with any person. To attach the necessity to a specific person, French uses either il faut que + subjunctive (Il faut que tu viennes, 'You must come' / 'You need to come') or the indirect-object construction il me/te/lui/nous/vous/leur faut + noun (Il me faut du temps, 'I need time'). Falloir has no personal conjugation whatsoever: forms like *je faux or *tu fauts do not exist.
A second group of fixed impersonal expressions works the same way: il reste (il me reste dix euros, 'I have ten euros left'), il manque (il manque deux chaises, 'two chairs are missing'), il existe (il existe plusieurs solutions, 'several solutions exist'), il semble que (il semble qu'il soit malade, 'it seems that he is ill'), and il vaut mieux + infinitive (il vaut mieux partir tôt, 'it's better to leave early'). The impersonal il est + adjective + de/que pattern belongs here too: il est important de réviser, il est nécessaire que tu répondes.
Il s'agit de deserves special attention because it is routinely mistranslated. It means 'it is a matter of / it is about', and its subject il can never be replaced by a real topic: you cannot say *ce livre s'agit de la guerre for 'this book is about war'. Instead French says Il s'agit de la guerre dans ce livre, Dans ce livre, il s'agit de la guerre, or simply switches verbs: Ce livre parle de la guerre / traite de la guerre.
Falloir que and several of these impersonal expressions of necessity, doubt, or possibility (il faut que, il semble que, il se peut que) are strong subjunctive triggers, so the clause they introduce takes the subjunctive: Il faut que tu viennes, not *que tu viens. Weather verbs and il y a, by contrast, take no complement clause and are simply invariable in form.
Rule of thumb: if the verb has no real, replaceable subject and only ever appears as il + verb, it is impersonal — never conjugate it for je/tu/nous, attach necessity to a person with il faut que + subjunctive or il me faut + noun, and remember that il s'agit de always keeps il as its subject, never the topic itself.
Examples
Il pleut depuis ce matin. — It has been raining since this morning. (Weather verb: il is a dummy subject with no real referent.)
Il faut que tu viennes à la réunion. — You need to come to the meeting. (Falloir attaches necessity to a person via il faut que + subjunctive (viennes).)
Il me faut encore un peu de temps. — I still need a bit more time. (Indirect-object construction il me faut + noun, an alternative to il faut que.)
Il s'agit d'un problème de sécurité, pas d'un simple retard. — It's a matter of security, not a simple delay. (Il s'agit de keeps il as its subject; never *ce problème s'agit de.)
Il vaut mieux réserver à l'avance. — It's better to book in advance. (Impersonal il vaut mieux + infinitive, expressing a recommendation.)
Il me reste dix minutes avant le départ du train. — I have ten minutes left before the train leaves. (Il reste is impersonal; the indirect object me identifies who the remaining time belongs to.)
Common mistakes
Je faux partir.
Il faut que je parte.
Falloir is impersonal: it exists only in the il form (il faut, il fallait, il faudra…) and never takes a personal subject like je, tu, or nous. To express that a specific person must do something, use il faut que + subjunctive (Il faut que je parte, 'I have to leave') or il me/te/lui faut + noun (Il me faut du temps, 'I need time'). There is no conjugation *je faux, *tu fauts.
Prerequisites
Related rules
impersonalfalloirsubjunctive-triggerweather