こそ
- 1Emphasizes a noun or phrase as precisely the one in question ('this very…,' '…for sure'), often implying a contrast with other cases.Ex. 1
- 2Attached to a verb's て-form, it means that something is achieved only by or only after doing that action.Ex. 2
Replacement: こそ replaces は and が rather than following them（今年こそ, not 今年はこそ）
Object marking: with を, both 名詞こそ and 名詞をこそ are possible
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こそ is used in both speech and writing to put strong focus on one element, often to express resolve ('this time for sure') or to say that one thing, and not others, is what counts. The fixed reply こちらこそ ('likewise, it is I who should…') is very common in everyday conversation. Compared with は, it is much more emphatic and exclusive.
Do not put こそ after は or が; it replaces them, though it can follow を, に, で and から.
Learners sometimes use こそ as a general intensifier, but it specifically singles out one item as the right or important one.
Note that in the て-form use, the main clause usually states a result that becomes possible only through that action.
- からこそN2「からこそ」is 「こそ」attached to the reason-marking 「から」, specifically emphasizing 'precisely because…'; it often pairs with 「のだ／んです」at the end of the sentence. 「てこそ」instead expresses the condition 'only if…', and the two cannot be swapped.
- てこそN2「てこそ」is the sense-2 usage of 「こそ」('only… then…'), typically followed by a judgment or evaluation; nouns and な-adjectives take 「でこそ／であってこそ」. The sense-1 'precisely' emphasis cannot be replaced with 「てこそ」.
- こそすれN3「こそすれ」is a fixed literary pattern attached to the masu-stem of verbs or する-nouns; the following clause must be negative, meaning 'only A, never B'. 「こそ」merely emphasizes the first item, with no negative requirement, so the two cannot be interchanged.
- さえN3「さえ」cites an extreme or minimal example to imply the rest, meaning 'even…', often paired with negatives, and can also mean 'even (in addition)'. 「こそ」only emphasizes the item itself. 「さえ」can directly replace 「が」or 「を」, and the two generally cannot be interchanged.
- はN5「は」simply raises a topic or marks contrast with a neutral tone, usable in ordinary statements; 「こそ」is heavy focus-emphasis. 「は」cannot express the usages of 「てこそ」or 「からこそ」. The two can combine as 「こそは」, but 「はこそ」is not possible.
からこそ ('precisely because') and てこそ ('only by doing') are specific combinations built on こそ, while こそすれ contrasts two things ('may well X, but certainly not Y'). さえ marks an extreme or unexpected example ('even') where こそ marks the most fitting one, and は simply marks a topic or mild contrast without こそ's strong emphasis.
