Substantivalism is the view that space is a real entity. A lot of substantivalists believe that there are (at least) two fundamental kinds – there is space and there are the material objects that occupy space. These kinds of objects are distinct from each other and equally real
It’s easier to understand what Substantivalism is by contrasting it with the main rival, relationalism. Relationalism is the view that all talk about space can be reduced to talk about the material objects that many substantivalists think occupy space. We don’t need space, says the relationalist. Space is not a real entity. Anything you say that you think commits you to the reality of space can be translated into talk about relations between objects.
The relationalist looks at the substantivalist and says, “You’ve got too many kinds of things in your ontology! You’ve got this stuff called space (whatever that is), and you’ve got these material objects. I can get by with just material objects. So I will.”
There is a third way to go. I was a little misleading above. I suggested that Substantivalism is the view that there are two kinds of substances – space and material objects. It is probably best to call that view Strong Substantivalism. Strong Substantivalists keep space and objects. Relationalists think this is unnecessary, and they get rid of space. You could agree with the relationalist that both kinds of substances are unnecessary, but instead of getting rid of space, you could get rid of material objects and reduce them to talk about space. This view maintains that space is a real genuine entity. Let’s call this view Weak Substantivalism. According to Weak Substantivalism, what we call material objects just are regions of space, and space is the real thing.
Ted Sider briefly mentions these two substantivalist views in Four-Dimensionalism (page 110). The main pro for Weak Substantivalism over Strong Substantivalism is that it posits the existence of fewer kinds of things. Of course there are some cons. Some odd sentences of English end up being true – e.g. A region of space-time bounded out the door and barked at the mailman.
Sider doesn’t think these cons are enough to give up on the view. I want to add some more things to the con list. I doubt the cons that I want to add to this list would persuade Sider, but they strike me as even more odd than the con listed above. I’ll post those cons soon.
I was wondering: would Newton be considered a Relationist and Leibniz a Substantivalist? I think I remember reading about a debate they had about space, and I think that I’m correct but it’s been so long so I’m unsure.
At first glance, this weak form of Substantivalism is remarkably odd. Material objects are just regions of space? Really? I think that even though the Strong Substantivalist has a more muddled ontology, that still seems more plausible to me than the weak. We strive for simple ontologies, yes, but not at the expense of coherence and plausibility.
Perhaps I need to read more into it.
It’s the other way around. Leibniz is the relationalist, and Newton is the substantivalist.