こそすれ〜ないAnd certainly not, But certainly not, But, Although, Even though

Occasionally in Japanese, the adverbial particle こそ will be seen followed by the realis form (sometimes referred to as the perfective form) of verbs. This is a classical verb form that does not have a modern counterpart. However, the hypothetical form has largely replaced the realis form in the manner in conjugates.

The verbs that will be seen altered this way are する ‘to do’, なる ‘to become’, and ある ‘to be’. They will respectively become こそすれ, こそなれ, and こそあれ , and are used specifically for emphasis. Common translations include ‘certainly not (B), but (A)’, or ‘even though (B), actually (A)’. The (B) phrase in this grammar point will include a negative statement, and is usually something that the speaker is responding to or correcting about what another person mistakenly thought.

こそすれ may attach to either the noun part of する-Verbs, or the conjunctive form of standard verbs.

なれ and あれ will be used based on the standard rules of what type of word なる would usually appear with (a noun or adjective), and what type of word ある would usually appear with (a noun).

Caution

There are cases where the base verb will have been entered in some way, like by having the causative or the passive auxiliary verbs attached to them before the new base will be altered with こそする. So you will need to work out what verb stem is actually being used in any given sentence.