立場とは「予算の6割が欲しい」といった要求そのもので、利害はその背後にある「新製品を期日までに出したい」「離職を防ぎたい」といった理由や必要性です。立場同士は衝突しても、利害は両立できることが多くあります。転換の手順は、①双方に「なぜその額が必要か」を問い、利害を列挙する、②共通の利害（会社全体の売上、顧客満足）と相反する利害を整理する、③複数の選択肢を評価せずに出す（予算の時期をずらす、共通リソースを共有する、成果連動で配分する）、④市場データや過去実績など客観的基準で選ぶ、です。人と問題を切り離し、相手を敵ではなく共同の問題解決者と位置づけることが前提となります。A position is the demand itself ("we need 60% of the budget"); an interest is the reason behind it ("we must ship the new product on schedule," "we need to stop attrition"). Positions collide, but interests can often be satisfied simultaneously. To shift: (1) ask each side why they need that amount and list the interests; (2) sort shared interests (company revenue, customer satisfaction) from conflicting ones; (3) generate multiple options without judging them—phasing the budget over time, sharing a common resource, allocating on performance milestones; (4) choose using objective criteria such as market data or past results. Throughout, separate the people from the problem and treat the other side as a joint problem-solver rather than an adversary.
フィッシャーとユーリーの『Getting to Yes』は、①人と問題を分離する、②立場ではなく利害に焦点を当てる、③双方の利益になる選択肢を生み出す、④客観的基準を用いる、の4原則を提示しました。立場交渉は「私は60%、あなたは40%」という一次元の綱引きになりやすく、譲歩の応酬で関係も損なわれます。利害を掘り下げると、例えば営業部門は第1四半期に集中投資したいのに対し、開発部門は年間を通じた安定予算を望むといった時間軸の違いが見つかり、配分の時期をずらす統合的な解決が可能になります。1978年のキャンプ・デービッド合意でシナイ半島の「主権」（エジプトの利害）と「安全保障」（イスラエルの利害）を分けて解決した事例が有名です。利害を聞き出すには「なぜ」「なぜそうしないのか」という問いと、相手の利害を言葉にして確認する傾聴が不可欠です。Getting to Yes sets out four principles: separate the people from the problem, focus on interests rather than positions, invent options for mutual gain, and insist on objective criteria. Positional bargaining collapses into a one-dimensional tug-of-war—"I want 60, you want 40"—and the cycle of concessions damages the relationship. Digging into interests often reveals different priorities: sales may need heavy first-quarter investment while engineering wants stable funding across the year, which makes phased allocation an integrative solution. The 1978 Camp David accords are the classic illustration: Egypt's interest was sovereignty over the Sinai, Israel's was security, and once separated from the position "who owns the land," a demilitarized Sinai under Egyptian sovereignty satisfied both. Eliciting interests requires asking "why" and "why not," and active listening that restates the other side's interests in your own words.
利害交渉は相手も協調的である場合に最も機能します。相手が強硬な立場交渉や駆け引きに終始する場合、こちらだけが利害を開示すると搾取される恐れがあります。また社内政治や面子が絡む場面では、本当の利害を口にすること自体が難しく、表向きの理由しか出てこないことも多いです。Interest-based negotiation works best when the other side cooperates. If they stick to hardball positional tactics, unilaterally disclosing your interests invites exploitation. In politically charged or face-sensitive settings, people often cannot voice their real interests and offer only official reasons.
利害の開示は段階的に行い、相手の開示に応じて深めましょう。相手が駆け引きを続けるときは「交渉ジュジツ（negotiation jujitsu）」として相手の攻撃を問題への攻撃と読み替え、「その提案の背景にある懸念は何ですか」と問い返します。第三者や事前の非公式対話で本音の利害を探る場も有効です。Disclose interests incrementally, matching the other side's openness. When they keep playing hardball, use what Fisher and Ury call negotiation jujitsu: reframe their attacks as attacks on the problem and ask, "What concern lies behind that proposal?" Informal pre-meetings or a neutral third party can also surface interests people will not state at the table.