Kiam eksonis la sonorilo, mi malfermis la pordon.

When the doorbell started ringing, I opened the door.

Breakdown of Kiam eksonis la sonorilo, mi malfermis la pordon.

• mi: I
• kiam: when
• malfermi: to open
• pordo: the door

Questions & Answers about Kiam eksonis la sonorilo, mi malfermis la pordon.

What does kiam do in this sentence?

Here kiam means when and introduces a time clause:

Kiam eksonis la sonorilo = When the bell rang

In Esperanto, kiam can be used both:

• in questions: Kiam vi venos? = When will you come?
• in subordinate clauses: Kiam li venis, mi foriris. = When he came, I left.

So in this sentence, it is not asking a question; it is linking two actions in time.

Why is it eksonis and not just sonis?

The prefix ek- usually means beginning suddenly or starting.

So:

• soni = to sound
• sonis = sounded / was sounding
• eksonis = started to sound, rang out, went off

With a bell, eksonis is very natural because a bell often begins ringing at a specific moment. It gives the sense of the bell started ringing rather than just the bell was making sound.

How do I know the sentence is in the past tense?