The Hidden Philosophies of Newton and Leibniz

Since the advent of modern science (beginning in the 16th century with Galileo), the division between practicing philosophy and practicing science has increasingly widened. Some would claim that this rift indicates that scientists no longer practice philosophy; however, whether or not they would acknowledge it, I’d assert that all scientists practice philosophy. In Chapter 2 of Lawrence Sklar’s Space, Time, and Spacetime, we are presented with a debate on the existence of spacetime, between Isaac Newton’s substantivalism and Gottfried Leibniz’s relationism. I first assert that Newton’s and Leibniz’s underlying philosophical worldviews are mechanical materialism and objective idealism, respectively. I then will explore a possible dialectical materialist approach to the question. To indicate why this approach is desirable, I will show that in fact, Newton’s mechanical materialism degenerates into objective idealism.

First, I will define a few key terms. Materialism as a philosophy claims that an objective, material reality made up of matter exists independent of consciousness, and that it is the foundation and determinant of thinking. Materialism is mechanical if it sees material as a set of wholly separate, discrete objects that act upon each other in a causal fashion, isolating matter from motion. Dialectical materialism, instead of emphasizing objects, emphasizes processes and relations; it sees the world not just as matter, but as matter in motion, integrated into complex structures. In contrast to materialism, idealism places primacy on consciousness and the senses over the material world. Specifically, objective idealism posits that ideas are not determined subjectively by the individual, but rather objectively (an example being Hegel’s Absolute Idea).

In his arguments for substantivalism, Newton takes on a mechanical-materialist framework. Sklar notes that “according to a Newtonian substantivalist… even if there were no matter in the universe whatever, there would still be space with its standard three-dimensional Euclidean structure” (160); further, “its persistence is characterized by its total unchangingness through time” (161). This conception of space severs it from the matter that inhabits it, conceiving of objects in a discrete and static way, neglecting processes and relationships. Sklar goes on to describe Newton’s belief in fixed coordinate points in this Euclidean space. This again isolates individual components from an integrated whole in a mechanical fashion; if these points ‘exist’, relative to what? How can we meaningfully talk about these “fixed points” when we can only talk about relative distance between material objects? Newton’s bucket argument is also mechanical (although a refutation of his argument is outside of the scope of my argument). Newton sees a set of discrete objects; thus, he searches for causal explanations of objects acting on one another, rather than also considering the structure as a whole. Newton avoids asking questions about more complex relationships between the objects, about the fluid motion of water particles in relation to each other, and the general integratedness of the entire physical system.

In contrast, Leibniz’s methodology is essentially objective-idealist. Sklar notes in passing that in Leibniz’s deeper metaphysics, “he believed not only that space was merely a set of relations among material things, but that, properly speaking, there weren’t really material things or spatiotemporal relations among them” (170). This solipsistic rejection of the material world is decisively idealist. Even though Sklar leaves these metaphysics aside to present Leibniz’s arguments, they cannot be separated from his framework. Leibniz’s first argument is epistemological; he asserts that since the position and motion of space cannot be observed, it must not exist. Although a compelling argument, it’s not quite enough; it rests on the determination of existence by an objective observer (objective idealism). Leibniz’s final argument is his most sophisticated; it states that theories that can distinguish two states of the world without uncovering the cause that one would exist over the other must be rejected. However, his logic rests on a rational, divine creator who causes the universe to be one way instead of another. Thus, his argument boils down to the existence of Rationality as an ideal form that precedes material existence; this is classic objective idealism.

In contrast to both frameworks, dialectical materialism sees material objects in motion and in relation to each other; thus, it would reject at least Newton’s version of substantival spacetime for neglecting the intrinsic relationships and processes between matter and the space that it inhabits. Does this make the dialectical materialist a relationist? Perhaps, but which relationism? Mach and Berkeley were relationists, but insisted that spatial relationships are a product of consciousness rather than having an objective existence. In Materialism and Empirio-Criticism, Vladimir Lenin, a major developer of dialectical materialism, states that

“…space and time are not mere forms of phenomena, but objectively real forms of being. There is nothing in the world but matter in motion, and matter in motion cannot move otherwise than in space and time. Human conceptions of space and time are relative, but these relative conceptions go to compound absolute truth.”

Lenin emphatically rejects at least Mach and Berkeley’s relationism. However, he is clear that matter and spacetime are inseparable, which runs counter to Newton’s idea of a static spacetime with an independent existence. Thus, dialectical materialism rejects Newtonian mechanicalism, but also rejects the objective idealism of Leibniz and subjective idealism of Mach and Berkeley; space has an objective existence as a feature of a complex structure.

Perhaps surprisingly, we find that Newton’s and Leibniz’s philosophies are two sides of the same coin. Newton has a mechanical conception of space and matter, but ends up asserting that the universe is as it is because God created it that way. This is objective idealism because it relies on the objective Idea (coming from God) as the determinant of the material world. This degeneration into objective idealism runs deeper. The claim that spacetime exists as a static, fixed object independent of matter separates features of the universe from each other, relying on an abstract idea of space without matter. Specifically, the existence of absolute “spatial coordinates” has no basis or consequence in material reality, and thus is objective idealism: the objective existence of an ideal form. Thus, both Newton and Leibniz, in the final instance, reject the primacy of the material world in favor of an objective-idealist,  theistic “root cause”. Thus, a dialectical materialist worldview, a worldview that recognizes complex systems and processes, may begin to look more desireable.

In the debates between substantivalism and relationism, we must constantly be asking ourselves: which substantivalism, and which relationism? Although the line of demarcation has been drawn, there is not necessarily a unifying framework on either side; Newton, Leibniz, Mach, Berkeley, etc. are each operating within their own philosophical frameworks. So, perhaps instead of asking ourselves whether or not one side is ‘correct’, we should probe the arguments that each philosopher makes and consider which understandings of the existence of spacetime are rooted in compelling philosophical worldviews.


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