先日，久しぶりに会った経済学者の友人と飲んでいて，下記のような疑問が頭をよぎりました．
ドラゴンボールで戦闘力のインフレが起こったのは周知の事実である．一方で，トランクスと悟天が簡単にスーパーサイヤ人になったことに対し，ベジータが「スーパーサイヤ人のバーゲンセールだな」
友人には飲みながらのしょうもない質問にも関わらず，インサイトのある回答をもらいました．どうもありがとう．さらに僕があやふやだったところに対して，チャットで補足説明までしてもらい，とても勉強になりました．いずれまた役に立つと思いますので，自分なりにまとめておきたいと思います．
下記の説明は，友人とのやり取りを元に，私の理解を加えて再構築した説明です．全ての間違いは私自身の理解のあやふやさによるところなので，おかしいところがあれば指摘して下さい．ドラゴンボール風に言えば，天津飯が「俺に技を見せてみろ，俺はどんどん強くなる」と言っていた小気味良いあの名場面のように，他人の技を見せてもらって，どんどん強くなりたいと思います．
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（１）戦闘力のインフレ，（２）スーパーサイヤ人のバーゲンセールはデフレ，
（１） について，厳密にはドラゴンボールでは，戦闘力は「インフレ」していない．何故なら，戦闘力が上がっているのは，悟空，ベジータなどのZ戦士のみである． 戦闘力５のオッサンは，セルが出てくるまで話が進んでも，おそらく戦闘力は５のままである．本当に社会全体がインフレしていれば，彼の戦闘力は５００００くらいに なってるはずだけど，そうではないことは明らかである．「戦闘力のインフレ」が適応されてるのは「Z戦士と敵のコミュニティー」だけであり，これを慣用的に 「戦闘力のインフレ」と呼んでいる．慣用的に使っているのは理解できるが，しかしこの規模感では「インフレ」よりも「この業界での物価指数の上昇」くらいがより適当な対応概念ではないだろうか．
（２）についても，バーゲンセールは個々の活動主体（個人や店舗など）に関わる概念なので，マクロの概念であるデフレと直接結びつけるのは誤解を招く．バーゲンセールは個々の主体の判断で行なわれることが多い．もちろん，牛丼屋の値段競争のように，個々の活動主体が，個に留まらず大きな主体（業界とか）に影響を与えることはあるが，それは別の話である．また「デフレ」という言葉自体が社会全体に関連する概念なので「牛丼業界がデフレ」という表現であっても違和感がある．
これらを踏まえて，スーパーサイヤ人になるにはある一定の戦闘力の閾値があるとする． 1 ドラゴンボールで起こったことは，戦闘力が上がりやすいコミュニティーにいた人（Z戦士）の戦闘力が，スーパーサイヤ人になる閾値（定数）を超えやす くなったということに他ならない．閾値に届きやすくなったコミュニティー内部の人間に取っては，感覚的に「バーゲンセール」と形容されるが，そのコミュニティー外の人に取っては（例えば，戦闘力が５から変化のない農民に取っては）何も変化を感じられない．これは社会全体で見たら，インフレでもデフレでもない．
明治時代の参政権の条件を考えると，類似性があって面白いかもしれない．一定以上の税金を納めることが参政権獲得の条件であるが，物価指数の上昇の著しい業界 2で働く25歳以上の男子に取っては，直接国税15円以上（定数）の基準を超えることがより簡単になったので「参政権のバーゲンセールだな」と言っていた旧華族などがいるかもしれない．一方で，収入の変化の少ない業界で働く人に取っては，その限りではなかったはず．この状況はインフレとは言えないし（強いて言うなら，特定業界の物価指数の上昇や，それに伴う賃金の上昇），15円の閾値が全ての人に取って届くものになったわけではなく，社会全体にとってデフレとも言えない．
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拙い理解でおかしなところがあるかもしれませんので，ぜひ何か気付いたことがあればご指摘頂けると嬉しいです．ところで，明治時代の参政権などは，分りやすくて面白い例だと思いました．さらに「ドラゴンボールで戦闘力のインフレが起こったのは周知の事実である」というような問題の第一文が軽く反駁されるなどは，問題提起をした冥利に尽きるものでした．
昨今の経済政策によってインフレ・デフレというのは言葉としてよく聞きますが，私はそもそもそれらの言葉がどのように使われるかすらも理解していなかったようです．言い訳すると，インフレ，デフレがマクロな概念であることは，（昔に）教科書を読んで聞いたことがあったし，知っていたつもりでした．しかしどんな分野でもそうですが，概念を聞いたことがあるのと，理解するのと，それをアプライして物事を考えられるのには，それぞれに大きな大きな差があるものです．また抽象的な概念は，自分の興味のある具体的な文脈（僕の場合はドラゴンボールとか）になぞらえてみると，より興味を持てます．経済の先生をやってる人は，ぜひ中間試験の extra credit などに，上記の問題を出してみて欲しいです．笑 どんな答えが返ってくるか，僕も興味あります．
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