Past Participles as Adjectives

A past participle is born from a verb — lesa "read" gives lesinn "read," loka "close" gives lokaður/lokað "closed" — but it can grow up to live a second life as an ordinary adjective. Lokuð búð "a closed shop," þreytt börn "tired children," skrifað bréf "a written letter": here the participle is doing exactly what góður "good" or kaldur "cold" does — sitting in front of a noun or after vera, and agreeing with it in gender, number, and case. This page is about that adjectival life: how participial adjectives decline, how many of them have drifted into fully lexicalised adjectives, and — the crucial structural point — how the same form is frozen as a supine after hafa but fully declining as an adjective. (The participle's job inside the perfect and passive is treated under Supine vs Past Participle and the passive overview; this page stays on its adjectival use.)

The two base shapes: -aður/-uð/-að and -inn/-in/-ið

Participial adjectives come in two families, by verb class. Weak verbs give the -aður / -uð / -að type (masc./fem./neut.): loka → lokaður, lokuð, lokað; þreyta → þreyttur, þreytt, þreytt. Strong verbs give the -inn / -in / -ið type: lesa → lesinn, lesin, lesið; brjóta → brotinn, brotin, brotið. These are not special endings — they are ordinary strong-adjective endings, the same family as þreyttur, kaldur, blár. So a participial adjective declines through the whole adjective paradigm exactly like any other adjective; nothing new has to be learned about the endings themselves.

Attributive use — in front of the noun

Used attributively (before a noun), the participial adjective agrees with that noun just as opnar "open" agrees in opnar dyr "open doors." Put a participle in the same slot and it behaves identically. The cleanest way to feel this is the open vs closed contrast on the same plural feminine noun dyr "doors":

Notice lokuð (fem. sg.), lokaðar (fem. pl. acc.), handskrifað (neut. sg.) — the participle changes shape to match the noun, the defining behaviour of an adjective. The supine lokað / skrifað could never do this.

Predicate use — after vera

Used predicatively (after vera "be" or another linking verb), the participial adjective agrees with the subject. This is the everyday hún er þreytt "she is tired," þetta er lokað "this is closed" pattern.

The fact that þreytt / þreyttir / lokuð change form is the whole point: an English speaker says "she is tired," "the boys were tired," "the pool is closed" with one invariant word each time, and must learn to flex the Icelandic participle to its subject.

Lexicalised participles — fully-fledged adjectives

Many participles have drifted away from their verb and become ordinary dictionary adjectives — you would not even think of the verb when you use them. þreyttur "tired" comes from the verb þreyta "to tire/wear out," but no Icelander parses it as a verb form; it is simply the adjective "tired." Likewise áhugaverður "interesting," þekktur "well-known, famous" (from þekkja "know"), menntaður "educated" (from mennta), vanur "accustomed." These are participial in origin but adjectival in every behaviour, including comparison (þreyttari "more tired," þekktastur "best-known").

Strong or weak — chosen as for any adjective

Because these are ordinary adjectives, they make the strong/weak choice on exactly the usual grounds: weak (the -i/-a endings) after the definite article or a demonstrative, strong elsewhere. Lokuð búð "a closed shop" (strong, indefinite) but lokaða búðin "the closed shop" (weak, after the article); þreytt barn "a tired child" but þreytta barnið "the tired child."

The split that surfaces again: supine vs adjective

Here is the structural heart of the page, and the thing English speakers most need. The same participle form lives two lives, and you must keep them apart:

• After hafa, it is the supine — invariant, frozen, no agreement: ég hef lesið bækurnar "I have read the books." It does not matter that bækurnar is feminine plural; the form stays lesið.
• As an adjective, it fully declines and agrees: lesnar bækur "read books," lesin bók "a read book," lesinn texti "a read text."

The same word lesa yields a frozen lesið after hafa and a flexing lesinn / lesin / lesið / lesnir / lesnar / lesin as an adjective. This is the participle/supine split — already introduced for the perfect and passive — re-emerging at the adjective level. Once you have decided which slot you are in, the behaviour follows automatically.

Common Mistakes

lokað is the supine/neuter-singular shape; with feminine plural dyrnar the predicate adjective is lokaðar. The participle agrees here.

English "the boys are tired" gives one invariant tired; Icelandic flexes it to masculine plural þreyttir.

This is the split in reverse: after hafa the form is the invariant supine lesið, never the declining adjective. Over-applying agreement here is the classic over-correction once learners discover participles agree.

In front of the noun the participle is an adjective and agrees: lesnar bækur. The supine lesið belongs only after hafa.

Participial adjectives obey the ordinary strong/weak rule: strong when indefinite (lokuð búð), weak after the article (lokaða búðin).

Key Takeaways

• A past participle can serve as an ordinary adjective, attributively (lokaðar dyr, handskrifað bréf) and predicatively (hún er þreytt), and it agrees in gender, number, and case.
• The two base shapes are -aður/-uð/-að (weak: lokaður) and -inn/-in/-ið (strong: lesinn) — ordinary strong-adjective endings.
• Many are lexicalised into plain adjectives (þreyttur "tired," áhugaverður "interesting," þekktur "well-known," vanur "accustomed") and even take comparison.
• The strong/weak choice is the usual one: strong when indefinite (lokuð búð), weak after the article (lokaða búðin).
• The key split: the same form is invariant as a supine after hafa (hef lesið) but fully declining as an adjective (lesnar bækur). Decide the slot first.