The present participle (participe présent) and the gerund (gérondif) are not two names for the same thing. Both are built from the same -ant form, but the only reliable way to tell them apart is to look at what that form is attached to, a noun, a clause, or the main verb, which is exactly what this post walks through.
Formed from the nous stem (drop -ons) + -ant. Three verbs have irregular stems: être → étant, avoir → ayant, savoir → sachant.
Replacing qui
When the -ant form describes a noun and can be swapped for a relative clause with qui, it is functioning as a present participle, and it stays invariable.
Students who come to class get better exam grades.
The comme construction
The present participle can also replace comme when it introduces a cause. Unlike the qui replacement above, it does not need to attach to a specific noun sitting inside the main clause, and the two verbs can either share a subject or have different subjects.
Different subjects
Comme la pluie tombait sans arrêt, ils ont joué au foot en salle.(As the rain kept falling, they played indoor soccer)
La pluie tombant sans arrêt, ils ont joué au foot en salle.(Same meaning, participe présent)
Same subject
Comme il était en retard, il s’est assis au fond de la salle.(Since he was late, he sat at the back of the room)
Étant en retard, il s’est assis au fond de la salle.(Same meaning, participe présent)
The gerund (gérondif)
Formation and the shared-subject rule
en + participe présent
The gerund expresses an action happening at the same time as another, and it requires the same subject for both verbs. This is the single most useful thing to check before using one.
En sortant de la salle de sport, j’ai vu ma collègue Michelle et son mari.(Correct: I was leaving the gym, I saw Michelle and her husband, same subject)
En sortant de la salle de sport, mon téléphone a sonné.(Incorrect: this implies the phone left the gym)
Alors que je sortais de la salle de sport, mon téléphone a sonné.(Fixed: while I was leaving the gym, my phone rang)
Beyond simple simultaneity, the gerund can also express manner, cause, or condition, depending on context.
Simultaneity
Je cours en écoutant de la musique.(I run while listening to music)
Tout en cuisinant, elle écoutait un podcast.(While cooking, she was listening to a podcast; tout en reinforces the simultaneity)
Manner or cause
Il a réussi son examen en révisant intelligemment.(He passed his exam by studying smartly)
J’ai pu finaliser mon projet en faisant des heures supplémentaires.(I was able to finish my project by working overtime; = parce que j’ai fait des heures supplémentaires)
Condition
En t’entraînant 2 à 3 heures par semaine, tu vas progresser très rapidement.(By training 2 to 3 hours a week, you'll improve very quickly; equivalent to si tu t’entraînes 2 à 3 heures par semaine)
En réservant maintenant, tu paieras moins cher.(By booking now, you'll pay less; equivalent to si tu réserves maintenant)
