Japanese Grammar

How to Express Doubts: かな, かしら, だろうか, and ではないか


We have started a new section named “Advanced Sentence Patterns.” This is the final section in our grammar reference. Through learning advanced sentence patterns, you can spice up your knowledge more and more. In this lesson, you will learn how to express doubts in various ways

Explanation for How to Express Doubts in Various Ways

Table of Contents
かな, かしら, and だろうか: Expressing “to Wonder”
のではないか: Expressing Uncertainty
だろう and ではないか: Seek the Listeners’ Confirmation

When it comes to expressing doubts, we have only explained about interrogative sentences so far. However, there are still other types, e.g. expressing doubts without making questions like “to wonder.” You can express such things by placing key words at the end of sentences. Let’s learn how they work.

かな, かしら, and だろうか: Expressing “to Wonder”

(Neutral) [I] wonder if Japan is cool.
(Feminine) [I] wonder if there are cows in India.
(Masculine) [I] wonder if it’s summer in Russia now.

かな, かしら, and だろうか indicate the speakers’ doubts and are the counterpart to “to wonder” in English. The difference between the three is whether it’s a masculine or a feminine expression. Regarding the conjugations, you can just attach them at the end of sentences. However be careful, you have to remove だ from the state-of-being style, i.e. 夏だかな is wrong. The explanatory のだ sometimes appears, but the meaning will remain the same.

When it comes to the polite form, only だろうか has its own でしょうか. That sounds neutral while だろうか sounds masculine. Regarding かな and かしら, they can just be attached to the end of the polite form, but this will sound unnatural if you are young.

ほんすずしいですかな。 => Sounds elderly
インドにはうしいますかしら。=> Sounds like a lady
いまロシアはなつでしょうか。=> Sounds neutral

When question words are used, you have to use the explanatory のだ. In this context, のだ doesn’t usually change to んだ except for some dialects.

[I] wonder how cold it is in Japan.
[I] wonder why Indian people eat curry.
[I] wonder what Russian special products are.

のではないか: Expressing Uncertainty

(I suspect) [I] will fail in the next exam.
(I suspect) [our] salary will decrease soon.
(I suppose) as for kanji, [the number] is over 2000.
(I suppose) English is easier than Japanese.
(I doubt) ghosts exist.
(I doubt) alcohol is good for health.

のではないか, which can be んじゃないか, indicates your uncertainty of your opinion or guess. For example, with the last example above, you guess alcohol is not good for health, but at the same time, you still think alcohol may be somewhat good for health. English translation doesn’t work well here. Let’s check some similar sentence patterns for the sake of better understanding. Note: this should be pronounced with rising intonation.

First of all, you can adjust formality by changing or omitting parts of のではないか, i.e. from の to ん, from では to んじゃ, and from ない to ないです or ありません. The omitted form sounds the most casual.


かもしれない, which expresses there are some possibilities, can indicate a very similar meaning to のではないか. The difference is that のではないか more subjectively express your opinion. Another difference is that のではないか cannot be used in subordinate clauses while かもしれない can be.

(I suspect) [I] will fail in the next exam.
[I] may fail in the next exam.
(I suspect) [our] salary will decrease soon.
[Our] salary may decrease soon.

のではないか is actually very similar to negative questions when you are using it with other people. All of the examples mean “isn’t that kanji wrong?” and are said on the premise that you think that kanji is wrong.


だろう and ではないか: Seek the Listeners’ Confirmation

ろくにはかえってくる(だろう / でしょう)。↑
Will [you] come back by 6:00pm, right?
よるごはんは一緒いっしょべる(だろう / でしょう)。↑
As for dinner, [we] will eat [it] together, right?

だろう has the function of confirming something in order to clear up doubts you have. For example, with the first example, you doubt if he/she will come back at 6:00pm. Since だろう sounds masculine, we recommend you use the polite form でしょう if you are female. For younger generations, it will sound more natural if you drop the last う. Note: this should be pronounced with rising intonation.

だろう and ではないか (or じゃないか) have a function for another aspect of confirmation, which is to confirm preconditions for coming main topics. For example, with the fourth example below, you can say something like “そのあね来月らいげつ結婚けっこんするんです (the sister will get married next month).” Note: when people speak casually, they customarily drop the last か of ではないか (the third example). When people speak politely, they pronounce it with flat intonation (the fourth example).

ほんには3種類さんしゅるい文字もじがある(だろう / でしょう)。↑
Japanese has three kinds of characters, right?
ゲンキというきょうしょっている(だろう / でしょう)。↑
[You] know a textbook named “Genki,” right?
The station is over there, right?
I have an elder sister, right?

There are functions which are not related to doubts. だろう and ではないか indicate blame. One important point here is intonation. By pronouncing them with flat intonation, you can distinguish the functions. *In writing, you need to judge the functions based on only the context.

(Blame) [I] said “don’t use your cellphone here,” right?
(Blame) [it] is dangerous. *said to point out what someone has done.

This is a function that only ではないか has, which is to indicate discovery. The explanatory のだ and the ta-form can express the same thing.

[I’ve noticed] as for tomorrow, lessons are off.
[I’ve noticed] as for tomorrow, lessons are off.
[I’ve noticed] as for tomorrow, lessons are off.


  1.      かな, かしら, and だろうか express “to wonder” in Japanese.
  2.      のではないか expresses uncertainty.
  3.      だろう confirms something to clear up doubts you have.
  4.      だろう and ではないか confirm preconditions for the coming main topics.
  5.      だろう and ではないか indicate blame.
  6.     ではないか indicates discovery just like the explanatory のだ and the ta-form.

Although the similar forms may confuse you, the sentence patterns are very important, especially, かな and だろう (でしょう) as they are very often heard in everyday life. In practice, like the sentence ending particles, they tend to get affected by dialects. For example, だろう becomes やろう in the Kansai region and is used by both male and female. Japanese dialects are too complicated to recognize at first sight. However, if you understand the functions of each sentence pattern, you can quickly figure it out by looking up the counterparts. Next, you will learn a sentence pattern related the explanatory のだ.