treysta ("to trust; to strengthen") is a verb you cannot use correctly without getting its case right, and the case is the one English never prepares you for. To trust someone, treysta takes the dative: ég treysti þér "I trust you" — not the accusative þig. To rely on / count on someone, you switch to treysta á + the accusative: treysta á einhvern. So the same English root "trust/rely" splits across two case frames in Icelandic, and the difference between them is precisely the difference between trusting a person and depending on them. On top of that, treysta has a concrete literal sense — "make strong, reinforce" (treysta böndin "strengthen the bonds") — and a middle form treystast meaning "dare." This page nails all three down. (Orthography: keep the y in treysta/treysti — the stem is treyst-, and the ey diphthong never u-umlauts.)
Conjugation
Class: weak, Class 2 (the -ti/-i preterite). Auxiliary: hafa — ég hef treyst "I have trusted." The stem treyst- already ends in -st, so the past adds just -i (treyst- + i → treysti). A consequence worth flagging up front: the 1sg present and 1sg past are identical — both treysti — so context (and adverbs like núna vs þá) tells the tenses apart.
| Principal parts | |
|---|---|
| Infinitive | að treysta |
| 1sg present | treysti |
| 1sg past | treysti |
| 3pl past | treystu |
| Supine | treyst |
| Person | Present (nútíð) | Past (þátíð) |
|---|---|---|
| ég | treysti | treysti |
| þú | treystir | treystir |
| hann / hún / það | treystir | treysti |
| við | treystum | treystum |
| þið | treystið | treystuð |
| þeir / þær / þau | treysta | treystu |
| Person | Present subjunctive | Past subjunctive |
|---|---|---|
| ég | treysti | treysti |
| þú | treystir | treystir |
| hann / hún / það | treysti | treysti |
| við | treystum | treystum |
| þið | treystið | treystuð |
| þeir / þær / þau | treysti | treystu |
| Non-finite & imperative | |
|---|---|
| Imperative (þú) | treystu! / treyst þú |
| Imperative (þið) | treystið! |
| Supine | treyst |
| Past participle (m/f/n) | treystur / treyst / treyst |
| Middle voice (miðmynd) | treystast — esp. treystast til "to dare / feel up to" |
treysta + DATIVE — "trust someone"
This is the form you will use most, and it is the one to burn in: to trust a person, treysta governs the dative. Ég treysti þér "I trust you," hún treystir honum "she trusts him," við treystum þeim ekki "we don't trust them." The object is the dative form of the pronoun or noun — þér, honum, henni, þeim; mömmu, lækninum — never the accusative. There is no preposition: the dative attaches directly to the verb.
Ég treysti þér fullkomlega — þú hefur aldrei svikið mig.
I trust you completely — you've never let me down. — treysta + DATIVE (þér), no preposition.
Hún treystir lækninum sínum og fer eftir öllum ráðum hans.
She trusts her doctor and follows all his advice. — dative object 'lækninum'.
Ég treysti honum ekki lengur eftir það sem gerðist.
I don't trust him anymore after what happened. — present (or past — same form 'treysti') + dative 'honum'.
treysta á + ACCUSATIVE — "rely on / count on"
Add the preposition á and the case flips to accusative: treysta á einhvern "rely on / count on someone," treysta á eitthvað "depend on something." The nuance shifts too — from believing in a person's integrity (plain dative treysta) to depending on someone or something to come through (treysta á + accusative). You treystir vini þínum (you trust your friend, dative), but you treystir á vin þinn to show up (you're counting on him, accusative).
Við treystum á þig — ekki klikka á þessu!
We're counting on you — don't drop the ball on this! — treysta á + ACCUSATIVE (þig).
Bændur treysta á gott veður yfir heyskapartímann.
Farmers depend on good weather over the haymaking season. — treysta á + accusative (gott veður).
Þú getur ekki alltaf treyst á heppnina.
You can't always rely on luck. — supine 'treyst' + á + accusative (heppnina).
The literal sense: treysta = "strengthen, reinforce"
treysta also keeps a concrete, non-mental meaning: to make strong, reinforce, secure. You treystir a knot, a friendship, a defence, the foundations — here the object is a plain accusative thing (no á, no dative person): treysta böndin "strengthen the bonds," treysta stöðu sína "strengthen one's position," treysta varnirnar "reinforce the defences." This is the original sense (think "make trusty/sturdy"), and the trust meaning grew out of it.
Heimsóknin treysti vináttuböndin milli þjóðanna.
The visit strengthened the bonds of friendship between the nations. — literal 'treysta' = reinforce; accusative object (vináttuböndin); preterite 'treysti'. (formal/journalistic)
Fyrirtækið treysti stöðu sína á markaðnum með nýju samningunum.
The company strengthened its market position with the new contracts. — 'treysta stöðu sína' = consolidate one's position.
The middle: treystast (til) — "dare, feel up to"
The -st middle treystast means "to dare to / feel able to / feel up to," almost always with til + genitive or til að + infinitive: treystast til að gera eitthvað "feel up to doing something," ég treysti mér ekki til þess "I don't feel up to it." Note the reflexive mér (dative) that often rides along: treysta sér til "trust oneself to (manage) something."
Ég treysti mér ekki til að keyra í þessari hálku.
I don't feel up to driving in this ice. — 'treysta sér til að' (with reflexive dative mér) = dare / feel able to.
Hún treystist ekki til að halda ræðuna fyrir framan svona marga.
She didn't dare give the speech in front of so many people. — middle 'treystast til að' = dare / feel up to.
Common Mistakes
❌ Ég treysti þig.
Wrong case — to trust a person, treysta takes the DATIVE, not the accusative. It must be 'ég treysti þér'.
✅ Ég treysti þér.
I trust you.
The single most important correction on this page. treysta + person = dative (þér, honum, henni, þeim). The accusative þig is simply ungrammatical here — this is a transfer error from English, which has no case marking on "you."
❌ Við treystum á þér.
Wrong case — with the preposition 'á', the object is ACCUSATIVE: 'við treystum á þig'. Dative belongs to plain treysta (no á).
✅ Við treystum á þig.
We're counting on you.
The mirror-image error: once you add á, the case must switch to accusative (þig, not þér). The á governs the accusative.
❌ Ég treystaði henni.
Incorrect — treysta is a Class-2 -ti verb, not an -aði verb; the past is 'treysti' (identical to the present).
✅ Ég treysti henni.
I trusted her. (also = 'I trust her' — same form)
There is no -aði here, and the past treysti looks identical to the present — the tense comes from context.
❌ Ég treysti til að gera þetta.
Incomplete — 'dare / feel up to' is the MIDDLE with a reflexive: 'ég treysti mér ekki til að…' or 'ég treystist ekki til að…'. Bare active 'treysta til' doesn't carry the 'dare' sense.
✅ Ég treysti mér ekki til að gera þetta.
I don't feel up to doing this.
"Dare / feel up to" needs either the reflexive (treysta sér til) or the -st middle (treystast til), not bare active treysta.
Key Takeaways
- treysti / treystir / treysti / treyst — a weak Class-2 verb. The 1sg present and past are identical (treysti); tense comes from context.
- treysta + DATIVE = "trust someone" (ég treysti þér) — not the accusative. This is the headline rule.
- treysta á + ACCUSATIVE = "rely on / count on" (treysta á þig). The á flips the case to accusative and shifts the meaning to depending on someone/something.
- Literal treysta = "strengthen, reinforce" with a plain accusative object (treysta böndin, treysta stöðu sína).
- The middle treystast (til) = "dare / feel up to," usually with reflexive mér/sér (ég treysti mér ekki til þess). Auxiliary is hafa: ég hef treyst.
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