Berkeley and Mach were relationists who attempted to take up and finish Leibniz’s arguments, especially when it came to inertial effects.
Both object to absolute space on the grounds put forward by Leibniz- namely PSR and PII. Absolutist talk is incomprehensible, just like ‘nelectricity’.
Berkeley says we cannot imagine a moving object without its moving relative to something else, so a purely absolute motion is inconceivable. He says that in the two globes example, without a material reference body, no motion in the globes can be conceived, so some other explanation must be used for the tension in the chord, or he notion of the tension is nonsense.
Mach takes a realist position. Nobody possesses the skills needed to make use of any speculative absolutist view. There is no need for it, this it is meaningless. We cannot properly conceive of motion in a world of only one object, and so we do not know how that object would behave. ‘We cannot know how K would act in the absence of A, B, C’. Newton is on no position to claim what would happen in such a situation.
Both say that the idea of positions in an absolute space are also nonsense for they are unobservable and unknowable, but, as has been said before, Absolute space does seem to have observable, inertial consequences- can we not say that inertial effects provide a realist, empirical proof of absolute space?. In response, the relationist must be able to explain these inertial effects in a relational way. Such a theory, it is said, would be stronger than Newton’s as it would be simpler, and much more meaningful as it would avoid untestable predictions.
Can Berkeley and Mach give us a strong relationist theory of Inertia?
What is absolute motion? Newton says it’s rotation in the reference frame of absolute space, but what could a relationist say?
Both Berkeley and Mach said that absolute motion was motion relative to the ‘fixed stars’. Instead of bringing in absolute space here, we just consider space to be confined to the heavens and fixed stars, which are considered, as far as we can observe, to be at rest.
Mach’s realist position led him to say talk of absolute space is meaningless, and even inertial effects can be explained in relational terms, for all that is observed is the bucket’s rotation relative to the Earth and other celestial bodies. Mach says the stars are not the reference frame (as Leibniz may have held), but the center of mass of the entire universe, so when we accelerate in a car, we will be pushed back in out seat relative to the universe as a whole; relative to the centre of mass (worked out be averaging masses and their location).
So, for Mach, if the universe was spun around the bucked, the inertial effect would be the same. According to PII, the universe would be the same, for no observable difference would be possible.
Mach disliked Newton’s liking for the absolute, but his ideas are much similar. He has a belief in the absolute importance of empiricism. He does not give a theory of how these inertial effects work, as Newton seems to, but believes that these effects will be caused by some gravitational-like force that acts only on accelerating bodies (relative to the centre mass of the universe). Viz. Matter takes the role of Newtonian absolute space.
Newton does ask how the heavens could curve the water, as Mach’s theory demands.
