英語構文・文法の土台第13回: 条件・仮定・後悔

中心イメージ

条件・仮定は、「現実との距離」を表す。

if は条件。would は仮の結果。could have や should have は過去に対する推測・後悔・反省に使う。

形	中心イメージ	例
If A, B will…	起きうる条件	If the test fails, I’ll fix it.
If A, B would…	仮の話	If we had more time, we would refactor it.
could have	そうだった可能性がある	This could have affected users.
should have	そうすべきだった	We should have added a test.
would have	そうなっていただろう	The deploy would have failed anyway.

ニュアンス比較

if / when

If the deployment fails, we'll roll back.
When the deployment finishes, I'll update the thread.

if は起きるか分からない条件。when は起きる前提のタイミング。

would / will

This will break existing users.
This would break existing users.

will は強い予測。would は仮定に乗せた予測なので、少し柔らかい。

should have / could have

We should have added a regression test.
This could have been caused by the migration.

should have は反省・後悔。「やるべきだった」。could have は可能性。「そうだったかもしれない」。

日本語トラップ

`will` を if 節に入れすぎる

NG: If the test will fail, I'll fix it.
OK: If the test fails, I'll fix it.

未来の条件でも、if 節の中は現在形にするのが基本。

反省が強く聞こえすぎる

Strong: You should have checked this.
Softer: We should have caught this in review.
Softer: We could have caught this with a regression test.

You should have ... は相手を責めているように聞こえやすい。ポストモーテムでは we や仕組みに寄せる。

仮定と現実を混ぜる

If we have more time, we can refactor it.       # これから時間があれば
If we had more time, we could refactor it.      # 今は時間がないが、もしあれば

過去形は時間の過去だけでなく、現実から距離を取る働きもある。

実務例文

Planning

If we keep the scope small, we can release this week.
If we had more time, we would clean up the whole module.
This would be easier if the API returned a typed error.

PR review

This could break existing import jobs.
We should have a test for this edge case.
If we move this into a helper, the main flow will be easier to read.

Incident

The issue could have affected users in Japan.
We should have caught this with a staging check.
If the error rate increases again, we'll roll back immediately.

3秒練習

日本語	英語
スコープを小さく保てば、今週リリースできます	If we keep the scope small, we can release this week.
もっと時間があれば、モジュール全体を整理できます	If we had more time, we could clean up the whole module.
これは既存のインポートジョブを壊すかもしれません	This could break existing import jobs.
これはステージングチェックで検知できたはずです	We should have caught this with a staging check.