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Theory of Law [epistemology]


I was talking with a Botanist friend of mine, and the question came up, what is the difference between a Law and a Theory? Is Evolution a Theory, just like Gravity? Isn’t Gravity a Law? Are Laws just Theories with simple mathematical proofs?

Simply put, Laws are the codifications of existing observations. Theories are our attempts to make sense of observations in such a way as to explain the Laws in a coherent fashion.

So, without getting into semantic complexities, yes, Gravity is a Theory developed by Newton to account for the Inverse Square Law of gravitational attraction. Natural Selection is a Theory developed by Darwin to account for the facts of evolution.

The word “theory” is used for a whole lot of constructs, ranging from your pet hypothesis of the day to something that is well supported by evidence. In general, when scientists talk about the theory of something, they mean the latter. Laws are defined in the context of facts that are definitive, immutable, and limited to the range of experimental procedures that are used in establishing them.

Laws are a dime a dozen. Only a few are called Fundamental Laws, like Newton’s Laws of Motion, or the constancy of the speed of light in vacuum, though even here, the former is not exactly a prominent component of Quantum Mechanics. Others have even more obvious limitations — the inverse square law of gravitational attraction does not hold close to black holes or massive fast rotating bodies; the inverse square law of illuminance breaks down when confronted with lasers; Snell’s Law of refraction gets superseded by Bragg’s Law of coherent scattering when light goes through a transmission grating; the Biot-Savart Law, which forms one of the foundations of Maxwell’s Theory of Electromagnetism and describes the magnetic field generated by an electric current, is valid only when the current is unchanging, etc.

Newton’s Theory of Gravitation superseded Aristotle’s theory of “everything in its natural place”, which was based on various laws such as “things that go up must come down”, “rain falls from the sky”, “steam rises”, etc. It is to Newton’s eternal credit that he figured out that there were limitations to the laws that lay underneath Aristotelian theory: for example, if you threw something hard enough and far enough, the ground could slope down just enough that even as it fell, it would not come back down (yes, Newton had worked out the principle behind artificial satellites). Einstein’s General Theory of Relativity went one step better and not only got the little details correct (e.g., the anomaly in the precession of Mercury’s perihelion), but has been highly successful in dealing with extreme cases (e.g., binary neutron star orbital decay).

Biologists generally don’t go in much for Laws like Physicists do (correct me if I am wrong), probably because there is so much detail in the world that we see around us that it is difficult to properly abstract the facts into simplified Laws. Nevertheless, there are discernible trends, for instance the uncanny gradation in the beaks of finches on the Galapagos islands, as Charles Darwin noticed in On the Origin of Species, and realized that it is possible for a given species to evolve by adapting to their environment. That observation led him to develop the Theory of Natural Selection as a way to explain the evolution of species. This theory has become quite firmly established now with the discovery of DNA and the genetic code.

So the hierarchy is pretty clear: there are observations, which are condensed into facts, and codified into laws. These laws are sought to be explained using testable hypotheses, which become accepted as theories when sufficient empirical evidence supports them.