Three of the most common verbs in Dutch are irregular in a way English speakers find slippery: weten ("to know a fact"), kunnen ("can / to be able"), and mogen ("may / to be allowed"). All three change their vowel in the past and all three take hebben. The two modals — kunnen and mogen — add a wrinkle English doesn't have: when they govern another verb in the perfect, they appear not as a participle but as a bare infinitive (Ik heb niet kunnen komen, "I haven't been able to come"). This "infinitivus pro participio" (IPP) is the single most important thing to learn here, because it overrides the participle forms you'd otherwise expect. This page lays out all three side by side.
Weten — "to know (a fact)" (irregular, HEBBEN)
Weten means "to know a fact or piece of information" — distinct from kennen, which means "to be acquainted with a person, place, or thing." You weet that the shop closes at six; you kent the shopkeeper. Its past is wist / wisten (a vowel change plus a -st ending — a mixed pattern), and its participle is geweten. It takes hebben.
Principal parts
| Infinitive | Simple past (sg.) | Past participle | Perfect auxiliary |
|---|---|---|---|
| weten | wist | geweten | hebben |
Classification: irregular (vowel change e → i plus the dental -st).
Present tense
| Person | Form | Note |
|---|---|---|
| ik | weet | bare stem (long ee) |
| jij / je | weet | stem already ends in -t; no second -t |
| (inversion) | weet je? | — |
| u | weet | formal |
| hij / zij / het | weet | stem already ends in -t |
| wij / jullie / zij | weten | = infinitive |
Simple past
| Person | Form |
|---|---|
| ik / jij / hij | wist |
| wij / jullie / zij | wisten |
Perfect (hebben + geweten)
| Person | Form |
|---|---|
| ik | heb geweten |
| hij / zij / het | heeft geweten |
| wij / jullie / zij | hebben geweten |
Ik weet niet waar mijn telefoon is.
I don't know where my phone is. — present 'weet'.
Ze wist het antwoord meteen.
She knew the answer right away. — past 'wist'.
Dat heb ik altijd al geweten.
I've always known that. — perfect 'heb geweten'.
Kunnen — "can / to be able" (irregular modal, HEBBEN)
Kunnen is irregular even in the present: the singular has the stem kan, not kun, while jij has the alternative kunt alongside the common kan. The past is kon / konden, the participle gekund. As a modal governing another verb, its perfect uses the infinitive (kunnen), not the participle — that's the IPP. Gekund only appears when kunnen stands alone with no second verb (Ik heb het nooit gekund, "I never could do it").
Principal parts
| Infinitive | Simple past (sg.) | Past participle | Perfect auxiliary |
|---|---|---|---|
| kunnen | kon | gekund (or infinitive: kunnen, in IPP) | hebben |
Classification: irregular modal.
Present tense
| Person | Form | Note |
|---|---|---|
| ik | kan | not 'kun' |
| jij / je | kunt / kan | both standard; 'kan' more colloquial |
| (inversion) | kun je? / kan je? | 'kun je' is the set form |
| u | kunt / kan | 'u kunt' more formal |
| hij / zij / het | kan | not 'kunt' |
| wij / jullie / zij | kunnen | = infinitive |
Simple past
| Person | Form |
|---|---|
| ik / jij / hij | kon |
| wij / jullie / zij | konden |
Perfect — the IPP construction
| Construction | Form |
|---|---|
| with a second verb (IPP → infinitive) | Ik heb niet kunnen komen. |
| standing alone (participle) | Ik heb het nooit gekund. |
Ik kan je morgen helpen.
I can help you tomorrow. — present 'kan'.
We konden de trein niet halen.
We couldn't catch the train. — past plural 'konden'.
Sorry, ik heb je gisteren niet kunnen bellen.
Sorry, I wasn't able to call you yesterday. — IPP: infinitive 'kunnen', not 'gekund'.
Mogen — "may / to be allowed" (irregular modal, HEBBEN)
Mogen means "to be allowed / to be permitted" (and, with graag dropped, "to like" — ik mag hem wel, "I quite like him"). Its singular present is mag for ik / jij / hij alike. The past is mocht / mochten, the participle gemogen. Like kunnen, it uses the infinitive (mogen) in the perfect when it governs another verb (IPP); gemogen surfaces only when mogen stands alone, usually meaning "liked."
Principal parts
| Infinitive | Simple past (sg.) | Past participle | Perfect auxiliary |
|---|---|---|---|
| mogen | mocht | gemogen (or infinitive: mogen, in IPP) | hebben |
Classification: irregular modal.
Present tense
| Person | Form | Note |
|---|---|---|
| ik | mag | — |
| jij / je | mag | not 'magt' |
| (inversion) | mag je? | — |
| u | mag | — |
| hij / zij / het | mag | — |
| wij / jullie / zij | mogen | = infinitive |
Simple past
| Person | Form |
|---|---|
| ik / jij / hij | mocht |
| wij / jullie / zij | mochten |
Perfect — the IPP construction
| Construction | Form |
|---|---|
| with a second verb (IPP → infinitive) | Ik heb niet mogen meedoen. |
| standing alone (participle, "liked") | Ik heb hem altijd gemogen. |
Mag ik even langs?
May I come past for a moment? — present 'mag'.
Als kind mocht ik nooit lang opblijven.
As a child I was never allowed to stay up late. — past 'mocht'.
Ze heeft als enige niet mogen stemmen.
She was the only one who wasn't allowed to vote. — IPP: infinitive 'mogen'.
All three at a glance
| Infinitive | Present (sg.) | Past (sg. / pl.) | Participle | Aux | English |
|---|---|---|---|---|---|
| weten | weet | wist / wisten | geweten | hebben | to know (a fact) |
| kunnen | kan / (jij) kunt | kon / konden | gekund (IPP: kunnen) | hebben | can / be able |
| mogen | mag | mocht / mochten | gemogen (IPP: mogen) | hebben | may / be allowed |
Common Mistakes
❌ Ik kun je vanavond bellen.
Incorrect — the 'ik' form is 'kan', never 'kun'. 'Kunt/kun' belongs to jij/u only.
✅ Ik kan je vanavond bellen.
I can call you this evening.
❌ Hij kunt heel goed koken.
Incorrect — the 'hij' form is 'kan', not 'kunt'.
✅ Hij kan heel goed koken.
He can cook really well.
❌ Ik heb niet gekund komen.
Incorrect — when a modal governs another verb, the perfect uses the infinitive (IPP): 'heb niet kunnen komen'.
✅ Ik heb niet kunnen komen.
I haven't been able to come.
❌ Ze heeft gisteren niet gemogen meedoen.
Incorrect — IPP again: 'heeft niet mogen meedoen', not 'gemogen meedoen'.
✅ Ze heeft gisteren niet mogen meedoen.
She wasn't allowed to take part yesterday.
❌ Ik ken niet dat de winkel vandaag dicht is.
Incorrect verb — knowing a fact is 'weten', not 'kennen': 'Ik weet niet...'.
✅ Ik weet niet of de winkel vandaag dicht is.
I don't know whether the shop is closed today.
Key Takeaways
- Weten ("know a fact"): weet → wist → geweten, hebben. Contrast with kennen ("be acquainted with").
- Kunnen: singular ik kan, jij kunt/kan, hij kan — never ik kun or hij kunt. Past kon/konden.
- Mogen: singular mag throughout. Past mocht/mochten.
- Both modals use IPP in the perfect: with a second verb they appear as the bare infinitive (kunnen, mogen), not the participle. The participles gekund / gemogen surface only when the modal stands alone.
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