Did Melanchthon describe the three uses of the law found in Loci Communes prior to Calvin in his Institutes?
Yes. In a 1534 commentary on the book of Colossians Melanchthon first wrote of the three uses of the law. A 1535 edition of the Loci Communes Theologici also described the three uses of the law. Calvin’s Institutes of the Christian Religion was first published in 1536.