I think that most of us agree that two forces in the third
law, or F and a, in the second law, appear simultaneously
in those problems we solved (inertial frames, rigid objects
etc.). In my opinion the "cause and effect" issue is essential
but it is not part of physics; it is philosophy. Questions like
"why does this or that happens?" would become meaningful
wihthout a belief that everything that happens is caused by
something else.
Ludwik Kowalski