5.2.2 Isaac Newton’s Rules of Reasoning in Natural Philosophy

Religious people are fond of pointing out how deeply pious Newton was. In fact, in his own non-conformist manner, he was. He was also an alchemist and serious student of Biblical prophesy, forecasting the end of the Earth in the year 2060. The economist, John Maynard Keynes came into possession of Newton’s research papers on alchemy. After studying them he concluded in an oft repeated quote, "Newton was not the first of the age of reason: he was the last of the magicians." He may well have spent more effort in his religious studies and publication than in scientific works (though it is only his contributions to science that are considered memorable today). That surprising fact needs to be considered in the context of the time in which he lived (late 1600’s). This was before most discoveries in biology, medicine, astronomy, geology, physics, and chemistry had been made. Many of today’s modern sciences had not even been invented. The gaps in knowledge were deep and wide, and there had been a long uninterrupted history of allowing God to fill those gaps. There was no viable competing theory to the traditional theistic one. Essentially everyone was a theist and a creationist. Only a few decades earlier, England practiced persecution and torture of those who disputed church doctrine (and on rare occasion, execution).

Newton, although very devout, had no tolerance for what he called “occult causes” both because he saw them as unnecessary and unhelpful. They had no explanatory power, but were simply excuses for explaining away what we didn’t yet understand. In his day, the nature of magnetism, electricity, gravity, cohesion, friction, thermodynamics, fermentation, cell biology, and other natural phenomena were not well understood. He envisioned that from the confusion that then reigned, laws of nature would emerge to resolve those mysteries. He criticized the Aristotelians for ascribing occult causes to incomprehensible natural phenomena by correctly observing that “such occult qualities put a stop to the improvement of natural philosophy, and therefore of late years have been rejected. To tell us that every species of things is endowed with an occult specific quality by which it acts and produces manifest effects is to tell us nothing”. Even so, he himself subscribed to two seemingly occult entities – the invisible force called “gravity”, and the luminiferous ether through which he believed light traveled.

However, it is important to keep in mind that he lived on the historical edge of the scientific revolution. During his lifetime, there was not a clear distinction between chemistry and alchemy, between the natural and the supernatural, between science and magic. He helped to refine those distinctions in many ways, not the least of which was an often reprinted work of just a few pages called “Rules of Reasoning in Philosophy”. It was a simple guide to help thoughtful observers make sense of their experiences in the natural world.

He enumerated four rules for understanding real world “natural philosophy” (i.e., science) problems as follows:

“1. We are to admit no more causes of natural things such as are both true and sufficient to explain their appearances. To this purpose the philosophers say, that Nature does nothing in vain, and more is in vain, when less will serve; for Nature is pleased with simplicity, and affects not the pomp of superfluous causes.”

This is his somewhat anthropomorphized, teleological version of Occam’s Razor - “do not multiply entities beyond necessity”. Just as the Golden Rule shows up again and again in different religions, Occam’s Razor has a way of reappearing in different forms in Science. It also goes by the “Law of Parsimony”. Briefly, it means - the simplest solution that explains the phenomenon is to be preferred. Experience shows that this principle has surprising explanatory power and leads to the correct answer much of the time.

“2. To the same natural effects we must, as far as possible, assign the same causes. As to respiration in a man, and in a beast; the descent of stones in Europe and in America; the light of our culinary fire and of the sun; the reflection of light in the earth, and in the planets."

In other words, causality is universal – the light from our candle is the same as the light from the sun, which is the same as the light from a distant galaxy. A falling rock follows the same laws as a planet falling in orbit around the sun. Without evidence to the contrary, we can justifiably infer that the same types of causes produce the same types of physical outcomes.

“3. Qualities of bodies are to be esteemed the universal qualities of all bodies whatsoever.”

The qualities and characteristics of objects we can experiment on should be considered the same as similar objects that we have never touched. Principles derived from clear evidence are valid, beyond doubt. We should have the discipline to follow the evidence and not turn our backs on facts in favor of a belief that may be more comfortable or familiar. Look to nature for guidance and let it direct our research rather than let our theories blind us to the evidence. The third of Newton’s rules presages later, similar restatements of the same concept such as the “Cosmological Principle” and the “Principle of Uniformity”.

“4. Propositions deduced from observation of phenomena should be viewed as accurate until other phenomena contradict them.”

Unless proven otherwise, the best theory that successfully explains the facts should be accepted, keeping in mind that all theories are provisional, subject to revision given new evidence. Acknowledging that new discoveries were possible, he cautioned that future discoveries might lead to improvements of existing theories. Going back to the quote, “the light of our culinary fire and of the sun”, at that time there was no theory of nuclear fusion. Now we know that a candle flame is not the same as a nuclear reaction. This last rule embraces improvements and changes to theories to accommodate new discoveries of this type. The fact that he envisioned that future discoveries of this type could and would be made testifies to the tremendous insight he showed in developing these amazing and impressive guidelines. For this reason, I find myself returning to these these four simple and inspiring rules of reasoning to review and contemplate.

These guidelines have been modified, recycled, enhanced, and restated in many different forms since Newton first proposed them. They were among the first of many attempts to provide a philosophical framework and justification for the process of drawing conclusions from what we see happening around us, and extrapolating that knowledge to the greater universe beyond.