Newton’s “Four Rules of Reasoning” in Philosophy

One of the crowning achievements of the methods and tools of science is their self-correcting systematic approach of interrogating nature and therefore of perpetually morphing one’s knowledge of the natural world in accordance with the ensuing evidence of reality. In this manner, the experimenter suspends and subverts any preconceived notions, personal prejudices, or certain interests, therefore precluding any biased influences that they might possibly engender. The experimenter sees the universe as is rather than as what his senses demand it to be. Ultimately, the experimenter is able to ground a conclusion that is based on evidence, reasoning, and logic.

Perhaps, the scientific method owes its impeccable success to its policy of subjecting tentative statements of empirical reality (hypotheses) to the strictest rigors of testing and experimentation. The scientific method recognizes and accounts for its own fallibility by continually failing to falsify the closest approximations to truth. It is the only system of thought that celebrates uncertainty and recognizes its importance to progress.

Indeed, the development of the scientific method can be attributed to the intellectual prowess of one of the greatest minds in history and one of its earliest practitioners, Sir Isaac Newton. The notable English physicist devised one of the most powerful scientific and analytical tools ever and in so doing, created the modern scientific method. Indeed, he transformed natural philosophy into natural science and introduced mathematics as a research tool. His iconic Principia outlines his descriptions of the way he thought science should be done. Newton stated his four “Rules of Reasoning in Philosophy” as:

  1. No more causes of natural things should be admitted than are both true and sufficient to explain their phenomena.
  2. Therefore, the causes assigned to natural effects of the same kind must be, so far as possible, the same.
  3. Those qualities of bodies that cannot be intended and remitted and that belong to all bodies on which experiments can be made, should be taken as qualities of all bodies universally.
  4. In experimental philosophy, propositions gathered from phenomena by induction should be considered either exactly or very nearly true not withstanding any contrary hypotheses, until yet other phenomena make such propositions either more exact or liable to exception.


Newton’s handwritten manuscript of the Principia. Source: The Royal Society

The first two laws employ a principle of parsimony in order to “admit no more causes of natural things than are both true and sufficient” and to attribute the same causes to “natural effects of the the same kind”. Rule 3 instructs the experimenter that if there are certain qualities a body possesses that cannot be intended (increased) and remitted (decreased), that is cannot be varied, and that can be experimentally applied to all bodies on earth, then these qualities, using inductive reasoning, can be inferred to be universal qualities of all bodies in the universe, even bodies that are beyond the confines of our senses. We can generalise the properties of unobservable objects with properties that can be experimentally applied to all objects on Earth. Rule 4 also uses the term induction, albeit in a different manner. Here, the experimenter can apply the experimental results to other cases in order to test reliability. The resulting “propositions” can be shown to be “liable to exceptions” that is, not correct, by virtue of newly discovered phenomena and can hence be falsified. Here, Newton instructs the experimenter to continue to accept the inferred proposition as almost exactly true, until another phenomena are discovered that would render such propositions as “liable to exceptions” or, on the contrary, that would support them still further. But, mere “contrary hypotheses” should not imperil the acceptance of propositions “gathered from phenomena by induction” and can be dismissed if not backed up by measurements from the phenomena. To Newton, a hypothesis was any proposition “that’s not deduced from phenomena” and thus cannot offer an infer-able truth, given that logical observation conclusions cannot be consequently derived. Newton defines phenomena as that which “can be seen and is perceptible” by the external senses or “contemplated in our minds by thinking”. In the Principia, he says:

“I have not as yet been able to discover the reason for these properties of                               gravity from phenomena, and I do not frame hypotheses. For whatever is not                       deduced from the phenomena must be called a hypothesis; and hypotheses,                         whether metaphysical or physical, or based on occult qualities, or mechanical, have            no place in experimental philosophy.”

Sir Isaac Newton, English physicist

Newton’s method was the first to employ both induction and deduction. Scientific laws must first be deduced from the phenomena and then consequently generalized by induction. The generalized induction is, thus far, the closest approximation to what’s true. However, the accepted propositions cannot be accorded absolute universal validity, as they are open to refinements and experiments.

Newton acknowledged that such a method of inductive reasoning would not always give rise to absolute certainty. He maintained however that it is able to produce “the highest evidence that propositions can have in this experimental philosophy.”

Sir Isaac Newton’s burial place at Westminster Abbey. The monumental inscription reads: “Mortals rejoice at so great an ornament of the human race.” Source: Westminster Abbey

By recognizing the role of mathematics and experimentation in natural philosophy and establishing a self-correcting systematic approach to interrogate nature for what is, Newton had established the basic rules for scientific inquiry that have so far persisted up until the present day and transformed the world. They are perhaps one of the most crowning achievements of the Scientific Revolution and serve as a testament to the ingenuity of this great thinker. The principles of the scientific method set forth by Newton and contemporaries of his age indeed form the edifice upon which the technological prowess of today’s civilisation rests.



Newton, Isaac. The Mathematical Principles of Natural Philosophy, tr. Andrew Motte. Amherst, NY: Prometheus, 1995.


Featured image source: BBC Britannica 





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