John Stuart Mill...on method

It is unphilosophical to construct a science out of a few of the agencies by which the phenomena are determined, and leave the rest to the routine of practice or the sagacity of conjecture. We ought either not to pretend to scientific forms or we ought to study all the determining agencies equally, and endeavor, as far as can be done, to include all of them within the pale of the science. Else we shall infallibly bestow a disproportionate attention upon those which our theory takes into account, while we misestimate the rest and probably underrate their importance.

- Logic, 1843