Les habitants ferment leurs fenêtres pour ne pas respirer la fumée.

Les habitants means the inhabitants – people who live in a particular place (a town, a village, a building, etc.).

• les habitants focuses on people as residents of that place.
• les gens is more general: just “people,” not necessarily tied to a place.
• les résidents also exists, but is more formal/administrative or used for people staying in hotels, care homes, etc.

So les habitants highlights that these are the people who live there and are affected as local residents.

In this sentence, ferment is the 3rd person plural of fermer (“to close”):

• Pronunciation: [fɛʁm] – the -ent at the end is silent. It sounds the same as ferme (he/she closes) or fermes (you close).

There is also a French noun un ferment (“a ferment,” “yeast,” or figuratively “a driving force”), pronounced [fɛʁ.mɑ̃], but that is a different word with a different pronunciation and meaning.

Here it’s clearly the verb, because it follows the subject Les habitants and makes sense in context: The inhabitants close…

French present tense is used:

1. For things happening right now:
   
   • They are closing their windows.
2. For general or repeated actions / habits:
   
   • They (usually) close their windows (whenever this happens).

Without more context, this can reasonably be read either as something happening now or as a general reaction whenever there is smoke.

If you wanted to be clearly in the future, you’d say:

• Les habitants fermeront leurs fenêtres… – The inhabitants will close their windows…

For a completed past action:

• Les habitants ont fermé leurs fenêtres… – The inhabitants closed their windows…

Leurs is the possessive adjective used when:

• The owner is plural: les habitants (= they, more than one person)
• The thing owned is plural: fenêtres (windows)

So: leurs fenêtres = their windows (windows belonging to them).

Compare:

• ses fenêtres

  • ses = his/her/its, used when the owner is singular.
  • You’d use ses fenêtres if the owner were one person:
    
    • L’habitant ferme ses fenêtres. – The inhabitant closes his/her windows.

• les fenêtres

  • Just “the windows,” with no explicit idea of who owns them:
    
    • Les habitants ferment les fenêtres. – The inhabitants close the windows (could be any windows: in the school, in the office, etc.).

Here we want to show that the windows belong to the inhabitants, so leurs fenêtres is the natural choice.

It’s plural because:

• Each inhabitant typically has more than one window, and
• We’re talking about all the windows being shut.

You could use the singular in special contexts:

• Les habitants ferment leur fenêtre.
  This would suggest each inhabitant has one window (for example, maybe everyone has a single small window in a dormitory). It’s grammatically possible but less realistic in most everyday contexts.

So leurs fenêtres is the normal way to say their windows when people likely have several.

Pour + infinitive expresses purpose: in order to / to (do something).

• pour respirer – in order to breathe / to breathe
• pour ne pas respirer – in order not to breathe / to avoid breathing

So pour ne pas respirer la fumée means “in order not to breathe the smoke” or more naturally, “so that they don’t breathe the smoke” / “to avoid breathing in the smoke.”

This is very common:

• Je ferme la porte pour ne pas déranger. – I close the door so as not to disturb (people).
• Mets un réveil pour ne pas oublier. – Set an alarm so you don’t forget.

With an infinitive (the “to _” form), the normal French word order for ne… pas is:

ne + pas + infinitive

So you say:

• ne pas manger – not to eat
• ne pas parler – not to speak
• ne pas respirer – not to breathe

You do not split ne and pas around the infinitive:
❌ ne respirer pas (wrong with an infinitive)

ne… pas goes around a conjugated verb:

• Ils ne respirent pas la fumée. – They do not breathe the smoke.

But with infinitives, the negative is treated as a block: ne pas + infinitive.

In French, infinitives can be directly negated with ne pas:

• ne pas + infinitive = not to + verb / to not + verb

You don’t need a conjugated verb there. The pattern is simply:

• pour ne pas respirer – in order not to breathe
• sans ne rien dire (formal/literary) – without saying anything
• ne pas fumer (on a sign) – do not smoke / no smoking

So here, respirer is the infinitive, and ne pas directly negates it. That’s fully correct and standard.

Both can express purpose, but there is a structural difference:

1. pour + infinitive (same subject)

   • Used when the subject of both actions is the same:
     
     • Les habitants ferment leurs fenêtres pour ne pas respirer la fumée.
       = The inhabitants close their windows in order not to breathe the smoke.
       (They close the windows; they avoid breathing the smoke.)

2. pour que + subjunctive (different or explicitly repeated subject)

   • Used when the subject is different, or you really want to mention it:
     
     • Les habitants ferment leurs fenêtres pour que leurs enfants ne respirent pas la fumée.
       – The inhabitants close their windows so that their children don’t breathe the smoke.
     • Je ferme la fenêtre pour qu’ils ne respirent pas la fumée.
       – I close the window so that they don’t breathe the smoke.

In your sentence, the subject is the same (les habitants), so pour ne pas respirer is the natural, simpler choice.

French almost always needs an article before a noun, so you don’t usually say bare fumée by itself.

Here are the main options and their nuances:

• la fumée – the smoke (a specific or known smoke)

  • Suggests the smoke from a particular source that is understood from context (e.g. a factory, a fire nearby).

• de la fumée – some smoke (an indefinite amount)

  • Could be used if you mean smoke in general, not a specific, identified smoke:
    
    • …pour ne pas respirer de la fumée. – to avoid breathing (any) smoke.

The original la fumée implies a specific smoke the inhabitants are aware of (for instance, from a fire or pollution event). If the context were more general (any kind of smoke), de la fumée would be more likely.

No, respirer can be used both:

1. Without an object – simply to breathe:

   • Respire profondément. – Breathe deeply.
   • Il a du mal à respirer. – He has trouble breathing.

2. With a direct object – to breathe something in:

   • respirer la fumée – breathe the smoke
   • respirer l’air pur – breathe the fresh air
   • respirer un parfum – breathe in a perfume/scent

In your sentence, la fumée is the direct object: it’s what they don’t want to breathe.

In informal spoken French, the ne is very often dropped, especially in everyday conversation:

• Written / careful: pour ne pas respirer la fumée
• Very common spoken: pour pas respirer la fumée

Both are widely understood, but:

• In writing, especially in anything formal or for learners, you should keep ne:
  
  • pour ne pas respirer la fumée
• In casual speech, you’ll often hear pour pas respirer la fumée and similar structures.

So the sentence you have is the standard, correct written form.