Phlogiston? Elan Vital? Caloric? Mention of any of these at a party, and Neil DeGrasse Tyson will be sure to take you out back and kick you in your essences. So why do "essences" have no place in science? In this episode we explore that question (and dive into some of the history behind this debate) by reading Chapter 6 of Conjectures and Refutations: A Note On Berkeley As Precursor Of Mach And Einstein.
In one corner, we have the estimable Sir Isaac Newton and Roger Coates (and of course Andre the Giant, upon whose shoulders they are standing), and in the other, we have Bishop Berkeley and Ernst Mach, looking to throw down at the speed of sound. Berkeley can't get Newton and his forces out of his head (literally), and boy oh boy is the fight ever on.
Everybody who reads this list of twenty-one theses must be struck by their modernity. They are surprisingly similar, especially in the criticism of Newton, to the philosophy of physics which Ernst Mach taught for many years in the conviction that it was new and revolutionary; in which he was followed by, for example, Joseph Petzold; and which had an immense influence on modern physics, especially on the Theory of Relativity.
(20) A general practical result—which I propose to call ‘Berkeley’s razor’—of this analysis of physics allows us a-priori to eliminate from physical science all essentialist explanations. If they have a mathematical and a predictive content they may be admitted qua mathematical hypotheses (while their essentialist interpretation is eliminated). If not, they may be ruled out altogether. This razor is sharper than Ockham’s: all entities are ruled out except those which are perceived.
No attempt was made to show how or why the forces acted, but gravitation being taken as due to a mere "force", speculators thought themselves at liberty to imagine any number of forces, attractive or repulsive, or alternating, varying as the distance,[4] or the square, cube, or higher power of the distance, etc. At last, Ruđer Bošković[5] got rid of atoms altogether, by supposing them to be the mere centre of forces exerted by a position or point only, where nothing existed but the power of exerting a force.[6]
Mach's antipathy to theorizing and to the invocation of "metaphysical" and therefore unprovable notions led him to some extreme opinions. In The Conservation of Energy he remarks: "We say now that water consists of hydrogen and oxygen, but this hydrogen and oxygen are merely thoughts or names which, at the sight of water, we keep ready to describe phenomena which are not present but which will appear again whenever, as we say, we decompose water.
- David Lindley, Boltzmann's Atom
In Mach's world, there was to be no such thing as "explaining" in the way scientists had always understood it. Mach even went so far as to argue that the traditional notion of cause and effect-that kicking a rock makes it move, that heating a gas makes it expand —was presumptuous and therefore to be denied scientific status.
- David Lindley, Boltzmann's Atom
But it was not always so. Well into the latter half of the 19th century, most scientists saw their essential task as the measurement and codification of phenomena they could investigate directly: the passage of sound waves through air, the expansion of gas when heated, the conversion of heat to motive power in a steam engine. A scientific law was a quantitative relationship between one observable phenomenon and another.
- David Lindley, Boltzmann's Atom
Increments 
