Two out of the three variables, pressure, temperature, and volume, can be independent, but the third is determined by the other two and the equation of state.
Which variable is held constant when we use the Gibbs free energy?
Would you tell me a second equation involving these two variables, so that I can solve for them?
When we go sailing today, the winds will be light and variable. Women are accused of having variable moods, but it's not true.