-о / -ла / -ло

The active verbal adjective (радни глаголски придев, often called the l-participle) is an essential verbal form used in compound tenses and moods such as the past tense (перфекат), conditional (потенцијал), and future exact (футур II).

1. Basic Endings
For regular verbs ending in a vowel before -ти, endings attach directly to the infinitive stem (e.g., чита-ти → чита-). For verbs in -сти or -ћи with consonant stems, the base is obtained from the root or 1st person singular aorist without -ох (e.g., могох → мог-; једох → јед-):

• Singular: Masculine: -о (after vowels, e.g., чита-о, and after lost dental stops, e.g., је-о) or -ао (after other consonants with fleeting а, e.g., мог-ао) | Feminine: -ла | Neuter: -ло
• Plural: Masculine: -ли | Feminine: -ле | Neuter: -ла

2. Sound Changes to Watch For

• Vocalization (L → O): Historically, the masculine singular ending was -l. At the end of a syllable, -l shifted to -o (e.g., чита- + -л → читао; ради- + -л → радио). The original -л- reappears before all vowel endings (читала, радили).
• Fleeting A (Непостојано А): When consonant stems retain their final consonant (such as velars), an epenthetic -а- breaks up the final consonant cluster in the masculine singular: мог- → могао (feminine: могла); рек- → рекао (feminine: рекла).
• Loss of Dental Consonants (Д/Т): Stem-final dental consonants -д and -т drop before -л- without inserting fleeting а: јести (stem јед-) → јео, јела; пасти (stem пад-) → пао, пала. In verbs like расти (stem раст-), т drops before -л- (feminine расла, neuter расло), but is retained in the masculine singular before fleeting -а-: растао.
• Irregular Stem in Ићи: Verbs based on ићи (see перфекат глагола на -ћи) use a suppletive stem with -ш-: ишао / ишла, дошао / дошла.

3. Subject Agreement in Context
Because this participle agrees with the subject in gender and number, female speakers use the feminine form in the first person (ја сам радила), while male speakers use the masculine form (ја сам радио). Important agreement rules to keep in mind:

• Polite Address (Ви): When addressing one person politely using polite Ви (see also слагање учтивог ви у перфекту), the participle must be plural: masculine plural -ли for a man (Јесте ли завршили, господине?) or feminine plural -ле for a woman (Јесте ли завршиле, госпођо?; common conversational usage also accepts завршили).
• Mixed Groups: When subjects of different genders are joined together (e.g., a man and a woman), the predicate defaults to the masculine plural: Марко и Ана су дошли.