How do we know how the responding variable changes for the manipulated variables in the formular PV=nRT(ideal gas law)?

An ideal gas approximately follows the ideal gas law which
gives the relation between pressure and temperature as pV= nRT, where p is the absolute
pressure of the gas; V is the volume of the gas; n is the amount of substance of the gas
in moles; R is the gas constant (which is 8.314472 J*K^-1*mol^-1 in SI units); and T is
the absolute temperature.

Now, here we can change any of
the variables in the equation, which includes the pressure, the temperature, the volume
and the amount of substance. The relation pV = nRT is only a relation between them. The
variables that are not manipulated are the ones that respond to the changes. So these
can be pressure, temperature and volume. The amount of substance does not change except
in the case where we allow the gas to escape from the enclosure or enter the
enclosure.