Why is the Rate of Profits an Independent Variable in Sraffa’s PCMC?

Within the first 33 pages of his book, Sraffa (1960) changes his numéraire twice and settles with the third one for the rest of the book. This, by itself, had broken from the classical tradition in a significant way, but with the final numéraire came another momentous rupture from the classical tradition in the shift from taking wages as ‘given’ from outside to taking the rate of profit as ‘given’. Both the cause and the theoretical significance of this move have not been well understood in the orthodox Sraffian literature. In this note, I try to clarify this issue. JEL Codes: B2, B5