Physical laws are no more real than logical axioms. Both are human constructs, started as models used to explain observations and grown to accommodate other interests. Just like the physical law F=ma is a model to explain why a heavier ball kicked with the same force does not speed up as much, the logical axiom of transitivity "explains" why if you can trade sheep X for sheep Y and sheep Y for sheep Z, it is OK to trade sheep X for sheep Z in many circumstances.