Breakdown of Я прочитал все пришедшие письма.
я
I
письмо
letter
прочитать
to read (perfective)
прийти
to arrive (on foot, pf)
Questions & Answers about Я прочитал все пришедшие письма.
How is the participle пришедшие formed?
It is the active past participle of the perfective verb прийти (to arrive). For verbs with irregular past tenses like прийти (where the past tense is пришёл), the participle is built on that same past tense stem. Here, the stem is пришед-, to which we add the participle suffix -ш- followed by the plural adjective ending -ие.
Why does пришедшие have the ending -ие?
Participles decline just like adjectives and must agree with the noun they modify in gender, number, and case. Here it modifies письма (letters), which is in the accusative plural because it is the direct object of the sentence. For inanimate plural nouns, the accusative ending for participles is -ие.
Could I use the imperfective form приходившие instead?
You could, but it would change the meaning. The perfective пришедшие means you read the specific letters that had already arrived and were sitting there as a completed result. The imperfective приходившие would focus on a repeated action, meaning you read the letters that used to arrive over a period of time in the past.
Why are there no commas around the participle here?
When a participle is a single word acting like a normal adjective, it goes right before the noun it modifies (пришедшие письма) and does not take commas. Commas are only required when the participle has its own dependent words (forming a participle phrase) and is placed after the noun it modifies.