Learn Hardcore Japanese: zisin ga okoru to, ie ga yuremasu. - When an earthquake occurs, the house shakes.

The particle と here is a conditional marker. It connects two clauses and means “when” or “whenever.” In 地震が起こると、家が揺れます, it expresses that as soon as an earthquake occurs, the house inevitably shakes. This と is used for automatic or natural consequences that regularly follow an event.

Why is が used instead of は with 地震?

In this sentence, が marks 地震 (earthquake) as the subject introducing new information or an event. Using は would turn 地震 into a known topic or add contrast, which doesn’t fit here. We want to say simply “when an earthquake occurs…,” so が is the natural choice.

Why is 家 marked with が and not を in 家が揺れます?

Because 揺れる is an intransitive verb meaning “to shake” (the subject shakes). Intransitive verbs take が to mark the thing undergoing the action. If you wanted to say “someone shakes the house,” you’d use the transitive 揺らす and mark 家 with を (e.g. 彼が家を揺らす).

What’s the difference between the intransitive verbs 起こる / 揺れる and their transitive counterparts?

• 起こる (intransitive) – “to occur” (an event happens by itself)
Transitive: 起こす – “to cause” or “to bring about” something.
• 揺れる (intransitive) – “to shake” (the subject shakes).
Transitive: 揺らす – “to shake” something deliberately.
In our sentence, both the earthquake and the house act without a direct agent causing them.

Can we use 地震が起きる instead of 地震が起こる?

Yes. 起きる can also mean “to occur,” and 地震が起きる is very common in everyday speech. The difference is slight: 起きる often feels more colloquial, while 起こる can sound a bit more formal or suited to written descriptions. Either is acceptable here.

Could we replace this と conditional with たら or another conditional? How do they differ?

You can say 地震が起こったら、家が揺れます.
– と implies a general, automatic consequence (every time an earthquake happens, the house shakes).
– たら is more neutral or hypothetical and can suggest “if/when” in a single instance or future possibility.
Other conditionals like ～ば or ～なら also work but carry their own nuances (e.g. なら emphasizes “if it’s true that…”).

Why is 揺れる in the polite ～ます form here? What would change if we used the plain form?

Using 揺れます makes the sentence polite, which is common in informational or public contexts. In casual speech, you’d switch to the plain form:
“地震が起こると、家が揺れる。”
The meaning stays the same; only the level of politeness changes.

What are the readings and dictionary forms of 起こる and 揺れます?

• 起こる is read おこる. It’s already in its dictionary (plain) form.
• 揺れます is the polite form of 揺れる (read ゆれる). To get the dictionary form, replace ます with る, giving 揺れる.
Full readings:

地震 (じしん)
が
起こる (おこる)
と、
家 (いえ)
が
揺れます (ゆれます)