のではないだろうか・
A careful way to give your opinion: you ask it as a question. Despite the ない, you think it is so.
in an essay
Children today are perhaps too busy.
in a meeting
I think it might be better to postpone the meeting until next week.
How to form it
Plain form + のではないだろうか／のではないかと思う
A noun or な-adjective takes な in place of だ: 理由なのではないか, 公平なのではないか.
Polite
…のではないでしょうか／のではないかと思います
The ない isn't "not"
English does the same thing: "Isn't that too expensive?" means you think it is. When you think something is not so, the negative goes before の.
I think he'll probably come.
You think he will.
I think he probably won't come.
You think he won't. The "not" is in 来ない.
Softer than と思う
と思います states your view. のではないかと思います offers the same view for discussion, so people reach for it to disagree or to suggest something politely.
I think this schedule is difficult.
Your view, stated.
I think this schedule may be difficult.
The same view, with room left for the other person.
Which of the two?
のではないだろうか puts the question to the reader. It belongs to essays, opinion columns and speeches. In an essay it marks the writer's own opinion, which is often what a reading-test question is after.
Perhaps the delayed initial response made the problem worse.
Could the fact that this system is not widely known also be a reason why so few people use it?
のではないかと思う says "I think" outright, and works in writing and in speech.
I think starting with a small group may actually have contributed to the success.
I think it might be fairer to hear from the person in charge first.
Spoken politely, or in an email, だろうか becomes でしょうか. This is the one for a meeting, a boss or a customer.
Don't we need a little more time?
In conversation
のでは shortens to んじゃ. Among friends the ending shrinks further, to んじゃないかな or just んじゃない？.
I think we may have gone the wrong way.
I think this might be a bit expensive.
If we leave now, shouldn't we have plenty of time?
Close neighbours
かもしれないN4
Says only that something is possible. You aren't putting it forward as your opinion.
There may still be some tickets left.
The short spoken endings, with no と思う after them. じゃない？ asks the other person to agree, and じゃないか presses a point.
Wouldn't it be more convenient to have tomorrow's meeting online?
ではあるまいかN2
The same question in a literary voice. You read it and don't hear it.
Might this system actually be harder to use for the very people who need support most?
Check yourself
1What does this mean?
彼女は
Choose an answer to see why.
2"I think we probably won't make it in time."
Choose an answer to see why.
3Which one fits?
この
Choose an answer to see why.
More detail
With 心配 in place of 思う
With 心配する, 不安になる or 疑う where 思う was, the same shape carries a fear or a suspicion.
I was afraid we wouldn't make it.
Without なの
After a noun or a な-adjective, なの is often left out.
Perhaps this is the cause.
In reports and papers
Academic writing steps back one more pace, with のではないかと思われる or のではないかと考えられる: "it would seem that…".
It would seem that this difference is due to age.
More sentences
Considering the experimental results, perhaps this hypothesis needs to be reconsidered.
Judging from the data, perhaps users place more importance on ease of use than on price.
Wouldn't it be better to wait a little longer?