I am placing this question on philosophy stack exchange because a mathematician wouldn't care, and a physicist would be extremely insulted.
Consider Newton's Law F=ma. First, I am observing this as a definition of force. from a philosophical standpoint (assuming that we have developed a presumably accurate understanding of a coordinate system - and thus acceleration) this begs the question, what is mass? Moreover, it is objectively impossible to verify; it is defined through the invention of undefined quantities. Therefore, any result produced will be true (assuming we use sound logic, of course) because our method of verification will be circular. Say we simply assume it is a characteristic of a body. What, then, is the objective value of this?
We often hail Newtonian mechanics as turning point in physics; but why is it any less brilliant or valid to simply "invent" a new relationship and call it a "law." I could say, for instance, that every body has a quantity called "blablabla" and that from now on, force is the quantity: F=blablabla^(a). Obviously, this is a bit of a silly example... just an illustration.