By fundamental I mean isothermal, adiabatic, or isobaric. My book says that in expansion the maximum work is associated with isothermal process. But if I observe the PV graph, I feel like the isobaric work done is maximum, since it has more area under its curve. Does it depend whether ΔV is constant or the supply of heat is constant. Also does it matter if the system is being compressed or expanded, A theoritical reasoning might be better than just a numerical example.