Teasing Master Takagi-san 😝 ・ Volume 1

I felt like writing something grammary today, so here’s something that took me a bit of time to grasp properly in my earlier grammar-learning days. I’ve written it in a way that hopefully makes it easier for others to learn than it was for me.

Reasoning with のだ

One of the trickier Japanese grammar structures for English natives to get used to is のだ.

Consider the following observations:

  • The streets are wet.
  • The package that was left on my doorstep is not there.
  • Five new lessons came up for me in WaniKani.

These are incomplete observations. We have observed the effect, but we do not know the cause.

Since the cause is unknown, we are left to reason what the cause is likely to have been.

  • It must have rained. (That’s why the streets are wet.)
  • Kouichi must have swiped another one of my packages. (That’s why the package is missing from my doorstep.)
  • I must have Guru’d a kanji in my last review session. (That’s why five new lessons came up.)

This type of reasoning (known in English as abductive reasoning) is where you work out the reason (cause) for your observation (result). Note that these reasons may not necessarily be correct. Perhaps a street sweeper washed the streets, maybe I had my package sent to the wrong address, and it could be that the WaniKani staff just shifted some vocabulary to a lower level.

In English, there isn’t anything built into the grammar to denote this kind of reasoning. In Japanese, there is.

  • “It rainedのだ.”
  • “Kouichi swiped my packageのだ.”
  • “I Guru’d a kanjiのだ.”

This reasoning is intended to explain the cause of what we’ve observed. Thus, you’ll see this grammar referred to as “the explanatory の”.

Note that のだ may appear as んだ or simply の. When following a noun+だ, the だ becomes な. This results in noun+なのだ and noun+なんだ, as well as noun+なの. This may also appear as なんだ, or simply as なの (at the end of a sentence).

Structurally, what’s happening is the sentence is being turned into a noun phrase with の, then だ is added to turn it into a noun sentence: “It is (that) [phrase].” A close approximation in English is to say “It’s because [phrase]”:

  • “The streets are wet. It’s because it must have rained.”
  • “The package that was left on my doorstep is not there. It’s because Kouichi must have swiped it. (Again…)”
  • “Five new lessons came up in WaniKani. It’s because I must have guru’d a kanji.”

It’s also used when you have the complete observation (you know the cause/reason), and you are informing someone who has an incomplete observation:

  • “(The streets are wet) [because] there was a flood.”
  • “(Your package is missing) [because] a bobcat took it.”

The explanatory の can also be asked as a question: “Is it that [phrase]?” “Is it because [phrase]?”

からかい上手の高木さん Example


Takagi says “Lend me your eraser. I forgot mineの.”

From the classmate’s perspective, he observes that Takagi is asking to borrow his eraser, but he doesn’t know why she’s asking. So from his perspective, his observation is incomplete. He knows the result (she’s asking to borrow his eraser), but he doesn’t know the cause (why she’s asking).

Thus, rather than simply saying “I forgot mine”, Takagi includes a の at the end: “It’s because I forgot mine.” This gives the reason she’s asking. If she simply said 「()しゴミ()して」 and left it at that (without giving the reason), the boy could respond by asking, 「(わす)れちゃったの?」 “Is it because you forgot yours?”

しろくまカフェ bis Example

Panda goes to visit Polar Bear, only to find Polar Bear holding a snowboard. This creates an incomplete observation. Panda observes Polar Bear holding a snowboard, but the cause (the reason why) he’s holding the snowboard is unknown.


Panda suggests a reason: “Are you going out somewhereの?” “Is it that you’re going out somewhere?”

Here, Panda uses の to ask for confirmation of whether his reasoning is correct.

チーズスイートホーム Example

When a young boy finds an exhausted kitten in the park, his mother brings the kitten back to their apartment. Later, they find the kitten sleeping in the entryway.


The boy asks, “Why is the kitty sleeping in the entrywayの?” He observes the kitten sleeping there, but the observation is incomplete because he doesn’t know the reason why. Thus he asks. “Why is it that the kitten is sleeping in the entryway?” “Because why is the kitten sleeping in the entryway?”

The mother replies, “Probably, because it’s a comfortable spot for the catの.” The mother has the same incomplete observation, so she suggests a reason. “Probably, it is that it’s a comfortable spot for the cat.” “Probably it’s because it’s a comfortable spot for the cat.”

よつばと! Example

Yotsuba’s father bought a couple of pastries for an afternoon snack. Yotsuba sneaks and eats hers early, then eats her father’s éclair as well. Realizing she did wrong, she runs next door for help.


After hearing the story, the neighbor asks, “Why did you eat your father’s, tooの?” Her incomplete observation is Yotsuba’s testimony to having eaten the éclair. She lacks the reason why Yotsuba did it. Thus she asks, “Why is it that you ate your father’s too?” “Because why did you eat your father’s too?”

ふらいんぐうぃっち Example

After getting off the intercity bus, Makoto is greeted by her cousin Kei.

Makoto’s incomplete observation is that her cousin is at the bus stop. The part she is unaware of is why he is there. She comes up with the most obvious reason, and asks it: “Did you come to pick me upのです?” “Is it that you came to pick me up?” “Is it because you came to pick me up?”

Note that there was never an exchange where Makoto asks why Kei is there. Asking if it’s the case that he’s picking her up implies that she’s inquiring as to the reason why he’s there.