variable must undergo a change or in some part of the experimental protocol; this can be either by imposition of a change , or with the holding of constant, written For the principle to hold with full generality, must be extensive or intensive accordingly as is so. Obviously, to give this scenario physical meaning, the 'driving' variable and the 'moderating' or 'feedback' variable must be subject to separate independent experimental controls and measurements. Explicit statement The principle can be stated in two ways, formally different, but substantially equivalent, and, in a sense, mutually 'reciprocal'. The two ways illustrate the Maxwell relations, and the stability of thermodynamic equilibrium according to the second law of thermodynamics, evident as the spread of energy amongst the state variables of the system in response to an imposed change. The two ways of statement share an 'index' experimental protocol (denoted that may be described as 'changed driver, feedback permitted'. Along with the driver change it imposes a constant with and allows the uncontrolled 'moderating' variable response along with the 'index' response of interest The two ways of statement differ in their respective compared protocols. One way posits a 'changed driver, no feedback' protocol (denoted The other way posits a 'fixed driver, imposed feedback' protocol (denoted ) 'Feedback' variable change blocked or permitted This way compares with to compare the effects of the imposed the change with and without feedback. The protocol prevents 'feedback' by enforcing that through an adjustment and it observes the 'no-feedback' response Provided that the observed response is indeed that then the principle states that . In other words, change in the 'moderating' state variable moderates the effect of the driving change in on the responding conjugate variable 'Driving' variable changed or unchanged This way also uses two experimental protocols, and , to compare the index effect with the effect of feedback alone. The 'index' protocol is executed first; the response of prime interest, is observed, and the response of the 'feedback' variable is also measured. With that knowledge, then the 'fixed driver, feedback imposed' protocol enforces that with the driving variable held fixed; the protocol also, through an adjustment imposes a change (learnt from the just previous measurement) in the 'feedback' variable, and measures the change Provided that the 'feedback' response is indeed that then the principle states that the signs of and are opposite. Again, in other words, change in the