Nearly 70 years ago H. B. Collins, editing the anonymous early Tudor Mass O quam suavis, and decoding the manuscripts obscure instructions explaining how the notes of the tenor were to be arrived at, became the first editor to face the problem of editing musica speculative a term which I define and discuss elsewhere, but which for present purposes we may briefly describe as music which is conceived and presented in an esoteric format for academic presentation (skill in musica speculativa and musica practica being required by Cambridge of candidates for their music degrees in the early years of the sixteenth century, indicating that musica speculativa involved something beyond simple compositional skill, musica practica Collins naturally and rightly concluded that the notes of the tenor of this mass were not performable in their manuscript layout, since they were presented to suit an esoteric purpose, arranged either with fictional lengths or in the wrong order, and they needed arrangement and realization to form part of an edition that would make sense to modern readers and performers. However, the mass would have been just as unperformable to musicians of the time, and even though no contemporary arrangement survives there can be no doubt that a sixteenth-century performance edition, at least of the tenor, would have been essential.