[noun] + こそすれ、〜ない [verb ます-stem] + こそすれ、〜ない
Note: The second clause is always negative, denying the opposite or a worse outcome.
こそすれ is a formal, emphatic expression meaning "may indeed… but certainly not the opposite" or "if anything… but never…". It is used to strongly affirm one thing while emphatically denying its opposite. The pattern emphasizes that the reality is A (or at least A), and absolutely not the contrary.
The structure is built from the emphatic particle こそ combined with the classical concessive form すれ (the 已然形/realis form of する), creating a meaning of "even though/if one does indeed…". The second clause is always negative, typically denying the opposite or a worse situation.
Noun/Verb + こそすれ、〜ない
The first clause states what is actually the case (emphasized with こそ), and the second clause denies the opposite possibility.
This pattern is similar in spirit to ~ことはあっても~ない ("there may be… but never…"), but こそすれ is more emphatic and literary. It shares the rhetorical force of こそ seen in other emphatic structures like ~からこそ and ~ばこそ.