Table of Contents
The Basics
でした is a past tense marker for nouns and な-adjectives. It tells us that the word it’s attached to is relevant to the past, kind of like the word “was” in English. So,「先生でした」means “was a teacher”, and「大変でした」means “was terrible”. でした is associated with the polite form, just like です.
Forming でした
In Japanese, all past tense markers end in 〜た. でした is formed by removing 〜す from です and adding した to the end:
で
す+ した = でした
And there you have it. 簡単でしたね！
Patterns of Use
At the End of a Sentence
でした occurs at the end of sentences, where it marks them as polite form and past tense. It’s used with nouns and な-adjectives, as well as some other words that don’t have their own polite past tense form. Let’s start by looking at でした with a noun:
- 昨日はペットのハムスターの誕生日でした。
- Yesterday was my hamster’s birthday.
In this sentence, でした tells us that the noun 誕生日 (birthday) is something that occurred in the past. Due to the polite form, this sentence sounds socially aware, rather than plainly informative, like it would sound with the plain form ending だった.
でした works exactly the same way with な-adjectives:
- ハムスターの誕生日会は素敵でした。
- The hamster’s birthday party was wonderful.
In this sentence, the な-adjective 素敵 (wonderful) is marked as both polite and past tense by でした. The party was wonderful, and the speaker feels the need to say this politely.
でした can also be used after verbs, when they are in the negative polite form:
- ハムスターはケーキを食べませんでした。
- The hamster did not eat cake.
In this sentence, the 〜ません, ending on the verb 食べません (not eat) tells us that it is in the negative polite form. 〜ません cannot be conjugated to show tense on its own, so we stick でした on the end to mark for the past tense. This adds the past tense “did” meaning that we see in the English translation.
In the Middle of a Sentence
When でした appears in the middle of a sentence, it means that there are actually two or more clauses within that sentence. A clause is essentially a sentence that exists inside or connected to another sentence. でした can appear in the middle of a sentence if there are two independent clauses that are joined together into one sentence:
- [A: 誕生日でした]–から–[B: ハムスターはケーキを食べるべきでした]。
- Because it was her birthday, the hamster should have eaten cake.
In this example sentence, there are two clauses, [A: 誕生日でした] and [B: ハムスターはケーキを食べるべきでした], which could stand on their own as independent sentences. They are connected by から, which tells us that clause A is the reason for clause B. から is part of a group of conjunctive particles that connect clauses together, such as が and けど and ので.
Because clause A and clause B would become independent sentences if から was removed, it is possible for both clauses to have different politeness levels. In the example above, they are the same; both marked as polite by でした at the end of each clause. However, it would be grammatical to change the ending of clause A to the plain form using だった, and then mark clause B as polite with でした:
- [A: 誕生日だった]–から–[B: ハムスターはケーキを食べるべきでした]。
- Because it was her birthday, the hamster should have eaten cake.
Even though clause A is marked with だった, this sentence feels polite overall, because the ending of the entire sentence is the most potent marker of politeness. While we can have clause A in the plain form and clause B in the polite form, the reverse is not possible:
- ❌[A: 誕生日でした]–から–[B: ハムスターはケーキを食べるべきだった]。
- Because it was her birthday, the hamster should have eaten cake.
It’s possible that someone could say this sentence in spoken Japanese for some reason, but it is definitely awkward to have the first clause more polite than the second. In general, you should avoid putting the polite clause before the plain form clause.
Beyond the Basics
でした in Questions
When asking a question that ends in でした, you have two options. You can add the question particle か, or you can simply use rising intonation to indicate that you’re asking a question.
- ハムスター、元気でしたか？
- Was the hamster doing well?
When か is used after the plain form だった, it can add a strong, assertive tone to the question. With でした though, か does not add any feeling of assertion. In fact, でしたか would be the preferred form in formal situations. でした with rising intonation does somehow feel softer than でしたか though, albeit not as formal.
でした for the Non-Past
Sometimes, でした is used to refer to things happening in the present, or even the future. In these cases though, the past tense meaning of でした adds a nuance that the information being discussed is something that was known from before the present moment.
For instance, でした can be used to express the surprise you feel when you suddenly remember something that you should have remembered:
- 今日はペットの蛇の誕生日でした！
- Today is my snake’s birthday!
A more literal translation of this sentence would actually be “Today was my snake’s birthday!” This use of the past tense emphasizes that it’s information you knew before, even though you’re talking about something that is currently happening. Choosing the polite でした over the plain form だった indicates that you are communicating this to someone else, rather than saying it to yourself.
This emphasis on past knowledge that でした adds to a sentence can be used to ask questions that the speaker feels they should know the answer to. For example, after seeing that your boss didn’t drink the coffee you brought her, you might say:
- コーヒー嫌いでした？
- You don’t like coffee?
By using でした, you imply that this is a topic you’ve discussed before, and in doing so you acknowledge that you should have remembered the answer.
Similarly, you can use でした in questions that you feel are so silly, you should know the answer to. Because it implies that you have probably already heard the answer before, でした highlights a sense of regret or sheepishness at having to ask the question:
- 今日、何日でした？
- What day is it today?
The particle っけ is often added to this use of でした:
- 今日、何日でしたっけ？
- What day is it today?
Common Mistakes
With Past Tense い-adjectives or Verbs
Unlike nouns and な-adjectives, い-adjectives and verbs can conjugate to show that they are past tense, all by themselves:
い-adjectives:
❌ 美味しいでした。 ⭕ 美味しかったです。 was delicious
Verbs:
❌ 食べるでした。 ⭕ 食べました。 ate
It can be especially hard to remember that い-adjectives take 〜かった for past tense rather than でした, since they still take です for politeness. Just try to remember that でした should only be used to mark a word as past tense if it cannot do it on it’s own.