START WITH THESE TWO SENTENCES
The difference at a glance
昨日、日本語を勉強しました。
I studied Japanese yesterday.
You are telling someone what you did.
昨日の夜7時は、日本語を勉強していました。
At 7 last night, I was studying Japanese.
You are describing what you were doing at that moment.
Both describe the past. The difference is whether you report the event or describe the activity in progress.
One study session, two ways to describe it.
Imagine you studied yesterday from 6 p.m. to 8 p.m. It is one study session, but you can talk about it in two ways.
The time is the same.
Your focus changes.
The whole event
勉強しました
Report what you did, from start to finish.
A moment inside it
勉強していました
Describe what you were doing at that time.
Look at the whole event.
昨日、夜6時から8時まで勉強しました。
Yesterday, I studied from 6 to 8 p.m.
You are reporting the study session as one event. It can last two hours and still be described with しました.
Look at a moment inside the event.
昨日の夜7時ごろは、勉強していました。
At around 7 last night, I was studying.
You are showing what was in progress at that time. This sentence does not tell us when you finished.
The key is your perspective. “A long action” versus “a short action” is not the rule.
しました is the polite past form of する. Other verbs follow the same contrast: 食べました／食べていました and 読みました／読んでいました.
What about past habits?
A habit repeats over time. ていました can describe that ongoing pattern, rather than one uninterrupted action.
子どものころ、毎日ゲームをしていました。
When I was a child, I used to play games every day.
This does not mean you played without ever stopping. The words 子どものころ and 毎日 help us understand it as a past habit.
Some verbs describe a state.
With 住む, the ている form describes living somewhere. Its past form tells us about that living situation in the past.
去年は大阪に住んでいました。
Last year, I was living in Osaka.
This is a natural choice when you want to describe where you were living. Avoid translating every ていました as “was doing.” Look at the verb and the situation together.
Try it yourself.
Choose the expression that best fits the perspective described.
1. Report your study session as one event.
昨日、2時間＿＿＿＿。
A. 勉強しましたB. 勉強していました
Show answer 1
A. 勉強しました。 You are presenting the two-hour session as a whole event. B can work in other contexts, but it gives a different perspective.
2. Explain what was happening when your friend called.
友達から電話が来たとき、＿＿＿＿。
A. 勉強しましたB. 勉強していました
Show answer 2
B. 勉強していました。 Your friend’s call gives us a moment inside the action. You were studying at that time.
Take this into your next sentence.
Think of something you did yesterday. Describe it as one event. Then choose a moment inside it and explain what you were doing.
You are practicing more than a form. You are choosing how to show someone what happened.
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Meet Hokuto & Haru
Hokuto
Hokuto has taught 10,000+ hours of one-on-one Japanese lessons. A former paramedic, he began teaching Japanese as a volunteer and founded STRIVE in 2025. His coaching focuses on helping learners use Japanese with confidence in real conversations.
Haru
Haru helps learners develop natural, respectful Japanese for everyday conversations. Working alongside Hokuto, she supports learners with regular feedback and guidance as they put their Japanese into practice.