The past participle passive can normally be formed only from transitive verbs. The masculine nominative of past participle passive is formed by adding -s to the infinitive form of active verb. The participle is used as adjective and has the same declension rules as adjectives.
Indefinite declension
| Masc., sing. | Fem., sing. | Masc., plur. | Fem., plur. | |
| Nominative | celt-s | celt-a | celt-i | celt-as |
| Genitive | celt-a | celt-as | celt-u | celt-u |
| Dative | celt-am | celt-ai | celt-iem | celt-ām |
| Accusative | celt-u | celt-u | celt-us | celt-ās |
| Locative | celt-ā | celt-ā | celt-os | celt-ās |
Definite declension
| Masc., sing. | Fem., sing. | Masc., plur. | Fem., plur. | |
| Nominative | celt-ais | celt-ā | celt-ie | celt-ās |
| Genitive | celt-ā | celt-ās | celt-o | celt-o |
| Dative | celt-ajam | celt-ajai | celt-ajiem | celt-ajām |
| Accusative | celt-o | celt-o | celt-os | celt-ās |
| Locative | celt-ājā | celt-ajā | celt-ajos | celt-ajās |