The empirical claim
Let me finish with a comment on the form of the empirical claims that Sraffian theory calls for. First of all, the nomological sentence
is far from being an empirical claim and not only that: It does not allow the formulation of any such claim because it does not connect the theoretical terms with non-theoretical ones.
Unlike Marx, who connects his concept of labor-value with observed prices through his Law of Value, Sraffa does not specify any such connection. Price system p, as determined by law (6), need not coincide with the system of prices actually observed in the marketplace. Marx claimed that the prices actually observed in the marketplace were a nomic modification of labor-values, but nobody seems to know if Sraffa was interested in connecting his systems of prices, wages and profit rates with any non-theoretic magnitudes, and which ones might these be. In particular, Sraffian prices, even if it were possible to determine them for a particular real-concrete productive system, are not connected by Sraffa to any ‘observable’ magnitude.An example of an empirical claim that might be made with Sraffa’s conceptual apparatus is something like this: that the actual prices of the productive structure under investigation ‘orbitate’ around the Sraffian prices. Indeed, according to Nicholas (2011: 158),
the implication of Sraffa’s analysis is that reproduction or equilibrium prices are centres of gravity for the movement of actual prices rather than, as for Marx, averages of actual prices.
But then Sraffa’s theory would have to introduce an additional sentence (law) specifying such a nomic connection between Sraffian and observed or actual prices. 
The logical structure of Sraffian economic theory 181 fundamental law (6).
The task of normal science is, precisely, to find such a system. If there are several such systems, the task is to find them all. Sraffa never said this but, if the production structure is observably reproducing itself, one of those systems must be actually operating under the observable motion of prices, wages and profit rates; the problem is then to determine that one. Another possibility is the normative use of such systems. But this requires something like a central planner choosing the system that is more convenient according to an exogenous criterion. And both uses require connecting the theoretical magnitudes with non-theoretic ones (relative to Sraffa’s theory).Hence, what is missing in Sraffa’s theory is a theoretical systematization, a nomological sentence relating systems (π, w, p) with empirically observed magnitudes (like observed prices, wage and benefit rates, or what have you). Sraffa never introduced such a sentence and so, up to this point, his theory is not quite yet an empirical scientific theory. If Sraffian prices could be determined for a given real-concrete productive system, these prices would be hovering above the economic process, without any declared connection to it. It is clear that no empirical claims can be made with the theory as it stands now.
11.6