Questions & Answers about Il tuo patrigno e il mio figliastro si sono incontrati.
Why do we use the definite article with singular family members here (il tuo patrigno, il mio figliastro)?
Usually, singular family members with possessive adjectives drop the definite article (like mio padre or tua madre). However, step-relatives such as patrigno (stepfather) and figliastro (stepson) are exceptions. Because they are considered derived or altered family terms, they always keep the article.
Do the endings of patrigno and figliastro have a specific grammatical purpose?
Yes, the suffixes -igno and -astro historically carry a modifying or slightly pejorative tone, transforming the root words padre (father) and figlio (son) into step-relatives. Because they are structurally "altered nouns," they trigger the exception to the family-member rule and force you to use the definite article.
Why does the sentence use si sono incontrati instead of hanno incontrato?
The sentence uses the reciprocal verb incontrarsi to mean that they met each other. All reciprocal and reflexive verbs take essere as their auxiliary verb in compound tenses. Because it uses essere, the past participle must agree with the masculine plural subject, ending in -i (incontrati).
How would the verb ending change if the stepfather were a stepmother (la tua matrigna)?