In Classical sonata form, the second group - usually in the dominant or relative major - is normally recapitulated in the tonic. This means that a composer of sonatas must choose whether to transpose the second group in the recapitulation up or down a fourth/fifth or sixth/third. What advice, then, would Mozart have offered if his pupil Thomas Attwood had asked him how to decide whether the second group should come back transposed up or down?