The majority Reformed position regarding the relationship between the old and new covenants in seventeenth century Britain may be summarized by the formula: same in substance but different in administration. There were disagreements, however, among those who held this position, particularly with respect to the differences between the covenants. In fact, the way in which some described those differences led the puritan John Ball to wonder how they could consistently maintain their belief that the old and new covenants are the same in substance. A similar bewilderment is produced by reading some contemporary authors, including Michael Horton and T. David Gordon, because while they have affirmed the Reformed formula as it is encapsulated in the Westminster Standards, they have also asserted that the Mosaic covenant is a different kind of covenant than the Abrahamic and new covenants. These authors resolve the tension created by holding these seemingly contradictory positions by placing the Mosaic covenant in the administration of the covenant of grace which is where the Reformed formula locates the differences between the old and new covenants. Other Reformed authors, such as Rowland Ward, John Fesko, Robert Letham, and the authors of the OPC Committee Report on Republication, have argued that there is a Reformed precedent for this understanding of the Reformed formula. This paper will seek to demonstrate the impropriety of using the Reformed formula as understood by the Westminster Standards to posit a works covenant in the administration of the covenant of grace by looking at the formula’s historic meaning and use, especially how it was understood and used in and around the time of the Westminster Assembly.