【英文】
Nancy Alvarez: ..... The unspoken assumption is that we will reciprocate and tell them all about our relationship situation. And that's just not their business, thank you very much. (実践ビジネス英語11月号 38頁)

【和訳】
「それに応えて、こちらも相手に自分の人間関係の状況についていろいろ話す」という暗黙の前提があるのです。でも、そういうことは彼らにまったく関係のないことであり、大きなお世話です。(実践ビジネス英語 39頁)

【unspoken assumptionの説明 on web】
unspoken assumptionについて net上見てみると次の例が best answerになっていた。?この例なら 大きなお世話と評価するようなことではないようだが.....、

Best Answer: It's when you assume something about someone or something, but don't vocalize it, you just think about it. Like you might assume it's windy outside, but you don't tell anyone.

【unspoken assumption 説明別解 on web】
これだと他人は自分と同じ考えを持っているとの前提でいること 暗黙の了解の犯す危険を示しているようだ。
Unoken Assumptions
by Adam Guerra
Fundamentally, assumptions are facts that we tentatively decide to accept as true so we can continue to make progress, even though we know those assumptions might end up being wrong. Assume standard temperature and pressure, or assume a frictionless plane, or assume a spherical cow(a). Rather than measuring exact temperatures and pressures, or coefficients of friction, or the shape of a cow, these assumptions allow us to continue working on our problem. If our assumption is way off (there’s no such thing as a spherical cow, after all), then our answer will also be way off(b). If our assumption is roughly accurate, our answer might be good enough for our purposes.
(a) spherical cow =
(b) way off = 1Far away. 2Far from the intended target; far away from an intention or aim; greatly mistaken, quite wrong. (adjective) US Distant.

It’s probably obvious by now how assumptions can both help and hinder your requirements work. That’s why assumptions should always be tracked and listed – that way everybody knows exactly what assumptions are being made, what is affected by an incorrect assumption, and how to update requirements based on faulty assumptions. This is exactly the process we use, and what we recommend to everybody.

The problem lies with assumptions that are unspoken. For example, if I ask somebody for directions, I am assuming that they know where things are located, but I am also assuming more basic things such as what language they speak. Assumptions that you believe are likely to be true are correspondingly catastrophic when it turns out that they’re wrong.

I experienced this recently with a client. I was talking to them about “business requirements,” which are typically high-level features that don’t account for the solution, which comes later. The client, of course, had their own twist on processes and documents, and what they called “business requirements” DID account for the solution. We had several meetings that were very confusing because despite the fact that we used the same language, that language meant different things to each of us.

If you and a colleague are having trouble coming to a consensus on something that seems basic or obvious, stop and try this: re-examine all of your assumptions, and check that you’re both talking about the same thing before continuing. You’ll be surprised how often you’ve simply made different assumptions.

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