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, moderation 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 moderation protocol (denoted  The other way posits a fixed driver, imposed moderation protocol (denoted )