以後・已後|いごigo[1]atamadaka (head-high)

1. noun, adverbafter this; from now on; hereafter
   以後いごこんなことはいたしません。↗

   I'll never do this again.
2. noun, adverbthereafter; since (then); afteresp. after あれ, それ or the -te form of a verb
   それ以後いご彼女かのじょに会あっていません。↗

   I haven't seen her since then.

• Synonym今後こんごNeutralFrom now onward, often with an eye to plans ahead, as in 「今後ともよろしく」; 以後 can also mark the time after a point in the past.
• Synonym以降いこうNeutralLargely interchangeable with 以後, as in 「5時以降」「震災以降」; for a resolute 'from now on', 以後 is the usual choice.
• SynonymこれからNeutralFrom now on; in everyday writing use 「これから」, and it is common in speech. 以後 is more formal and can also follow a point in the past.
• SynonymのちWrittenRead 「しりえ」: an old word for the rear or behind — purely spatial, unlike 以後, which marks time after a point.
• Synonym向後こうごWrittenAn old-fashioned word for hereafter, found in old letters and official documents; it matches 以後's 'from now on' sense, but say 「今後」 in everyday use.
• Synonym後々あとあとNeutralLater on, well into the future, as in 「後々困る」「後々のため」; 以後 stresses all the time following a given point.
• Related将来しょうらいNeutralThe future or one's prospects, with a more distant horizon, as in 「将来の夢」; 以後 centers on the time after a set point.
• Related先々さきざきNeutralThe distant future, and also the various places one goes, as in 「行く先々で」; 以後 only marks time after a point.
• Related後々のちのちNeutralLater on, well into the future, as in 「後々困る」「後々のため」; 以後 stresses all the time following a given point.
• Related後あとWrittenRead 「しりえ」: an old word for the rear or behind — purely spatial, unlike 以後, which marks time after a point.
• Related未来みらいNeutralThe era yet to come, often the distant future, as in 「未来の社会」; 以後 centers on the time after a given moment.
• Related先行きさきゆきNeutralHow things will go from here — prospects, as in 「景気の先行き」; 以後 is purely temporal and says nothing about outlook.
• Relatedこの先このさきNeutralFrom here on; can also point to space ahead. Common in speech, while 以後 is time only and sounds more formal.
• Relatedこの後このあとNeutralMostly 'right after this' or before long, as in 「この後会議がある」; 以後 is more formal and stresses continuity from a point on.
• Related後来こうらいWrittenMeans hereafter and can also mean latecomers, but is rare in writing; 以後 or 「今後」 is the normal choice.
• Antonym以前いぜんNeutralThe antonym: before a given time or in the past, as in 「3時以前」「以前住んでいた」 — opposite to 以後 in time order.

Use 「以後」 for the time after a point or from now on, as in 「以後気をつけます」. 「以降」 is mostly interchangeable. For the time ahead also say 「今後」 or 「これから」; for the more distant future, 「将来」. Others are narrower: colloquial 「この先」「この後」, prospects 「先行き」, spatial 「後方」, old-fashioned 「向後」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. その時ときをいれて、その時ときから後あと。その後あと。