Nuance importante : COULD au passe exprime une capacite generale. Pour une action specifique reussie, on utilise was/were able to : "I was able to escape the fire." (J'ai reussi a echapper a l'incendie.)
B. Demander la permission
Modal
Exemple
Niveau de politesse
CAN
Can I borrow your pen?
Informel - entre amis, collegues proches
COULD
Could I borrow your pen?
Poli - avec des inconnus, en reunion
MAY
May I borrow your pen?
Tres formel - avec un superieur, en ceremonie
Echelle de politesse :
Can I...? (amical) < Could I...? (poli) < May I...? (tres formel)
C. Exprimer la possibilite
Modal
Exemple
Degre de probabilite
CAN
It can be very cold in winter.
Possibilite generale / theorique (parfois)
COULD
It could rain tomorrow.
Possibilite incertaine (~30-40%)
MAY
It may rain tomorrow.
Possibilite reelle (~50%)
MIGHT
It might rain tomorrow.
Possibilite faible (~30%)
A retenir : MAY exprime une probabilite plus forte que COULD ou MIGHT. "It may happen" = "Il est possible que cela arrive" (probabilite moderee). "It could happen" = "Ca pourrait arriver" (plus incertain).
D. Faire une suggestion ou une offre
Modal
Exemple
Nuance
CAN
I can help you with that.
Offre directe, capacite reelle
COULD
I could help you with that.
Suggestion plus douce, conditionnelle
MAY
Non utilise pour les offres
—
3. Formes negatives comparees
Affirmatif
Negatif
Sens
I can do it.
I can't / cannot do it.
Incapacite / Interdiction
I could do it.
I couldn't do it.
Incapacite passee / Impossibilite
It may happen.
It may not happen.
Possibilite negative (pas de contraction !)
Attention : "May not" ne se contracte PAS en "mayn't" (forme archaique quasi inexistante). On dit toujours "may not" en entier.
4. Tableau de decision rapide
Vous voulez dire...
Utilisez
Exemple
Je sais faire (present)
CAN
I can cook.
Je savais faire (passe)
COULD
I could cook when I was 10.
Est-ce que je peux ? (ami)
CAN
Can I sit here?
Est-ce que je peux ? (poli)
COULD
Could I sit here?
Est-ce que je peux ? (formel)
MAY
May I sit here?
C'est possible (theorique)
CAN
Accidents can happen.
C'est possible (reel, ~50%)
MAY
She may come tonight.
C'est possible (incertain)
COULD / MIGHT
It could/might work.
Ce n'est pas possible
CAN'T
That can't be right!
5. Pieges frequents des francophones
Erreur francophone
Correction
Explication
"I could swim yesterday" (action specifique)
I was able to / managed to swim yesterday.
COULD = capacite generale passee, pas une action precise
"Can I?" en entretien d'embauche
May I? / Could I?
Contexte formel = MAY ou COULD
"It can rain tomorrow"
It may/could rain tomorrow.
CAN = possibilite theorique, pas prediction
"May you help me?"
Can/Could you help me?
MAY ne s'utilise pas pour les requetes a autrui
Regle d'or : En cas de doute entre CAN, COULD et MAY, posez-vous cette question : "Est-ce que je parle de capacite, de permission ou de possibilite ?" puis "Est-ce que le contexte est formel ou informel ?"