"There is no earthly reason why a solo string instrument or voice, having the possibility to play or sing pure intonation, should want, or try, to be tempered"

In this quote, Lara St. John is expressing her belief that there is no logical or practical reason for a solo string instrument or voice to deviate from pure intonation. Pure modulation describes the precise and accurate tuning of musical notes, with no modifications or compromises. St. John argues that these instruments and voices have the capability to produce perfect modulation, and therefore, there is no need for them to conform to the tempered tuning system, which involves small modifications to attain a more standardized sound. She suggests that the pursuit of pure intonation ought to be the ultimate goal for these solo entertainers, rather than conforming to social norms or expectations.