The equation is not in a causal form, I will grant. But:
If I hold n and V constant and change T, it tells me what change I caused to P by changing T.
If I hold n and P constant and change V, it tells me what change I caused to T by changing V.
And so on.
The equation is just an equation. But if I control some of the parameters, I can still cause stuff to happen, and the equation tells me what stuff I will cause.
If I hold n and V constant and change T, it tells me what change I caused to P by changing T.
If I hold n and P constant and change V, it tells me what change I caused to T by changing V.
And so on.
The equation is just an equation. But if I control some of the parameters, I can still cause stuff to happen, and the equation tells me what stuff I will cause.