Когда я подошёл к двери, домофон снова зазвонил.

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Breakdown of Когда я подошёл к двери, домофон снова зазвонил.

• дверь: the door
• к: to
• когда: when

Questions & Answers about Когда я подошёл к двери, домофон снова зазвонил.

Why is it подошёл, and what does it imply here?

Подошёл is the masculine past-tense form of подойти, a perfective verb meaning to come up to / approach / walk up to.

Here it implies a completed movement: the speaker reached the door. It is not just was walking toward the door, but got to the door.

Compare:

• я подходил к двери = I was approaching the door / I used to approach the door
• я подошёл к двери = I approached the door / I came up to the door

Because this sentence describes one completed event in the past, подошёл is the natural choice.

Why is it к двери and not к дверь?

The preposition к requires the dative case.

So:

• дверь = door (dictionary form, nominative)
• к двери = to the door / toward the door (dative)

This is a very common pattern:

• к дому = to the house
• к окну = to the window
• к человеку = to the person

So подойти к двери is the standard way to say approach the door.

Why does двери end in -и? Isn’t that also a plural form?