Я пишу сообщение другу.

the friend

Breakdown of Я пишу сообщение другу.

• я: I
• писать: to write
• сообщение: the message

Questions & Answers about Я пишу сообщение другу.

Why is другу in the dative case? When do we use the dative case?

Because Russian uses cases to show grammatical roles. другу is in the dative case to mark the indirect object (“to whom” the message is written). друг (friend) is declined:

• nom друг
• gen друга
• dat другу
• acc друга
• inst другом
• prep друге
  Use the dative for recipients, like “to someone.”

Why is сообщение in the accusative case?

Because it’s the direct object – what you are writing. сообщение is a neuter inanimate noun, so its accusative form is identical to the nominative: сообщение.

Why isn’t there a preposition “to” before другу?

In Russian, cases replace many English prepositions. The dative case alone conveys “to someone,” so no separate preposition is needed.

What is the infinitive and aspect of пишу? How is it conjugated?

The infinitive is писать (imperfective). Imperfective verbs denote ongoing or habitual actions. Conjugation in the present tense:
я пишу
ты пишешь
он/она пишет
мы пишем
вы пишете
они пишут