Monday, July 1, 2019

Presentism, change and ontology

Presentism says that only present things exist. This by itself cannot explain the nature of change.

For assume an ontology on which, necessarily, everything that exists is either a concrete substance or a necessary abstract object. Consider a world w1 where all the concrete substances exist for all time, but some of them are changing their properties, e.g., shape. Notice that the presentist, the growing blocker and the eternalist all agree about what exists at w1, since no entity comes into or out of existence on this ontology, and hence the differences between the three theories are irrelevant to w1. Yet, w1 is a world with change.

Hence presentism by itself cannot explain change.

Perhaps someone who thinks that presentism is needed to explain change should opt for a trope ontology rather than a substance-and-abstracta or substance-only ontology. For then they can say that at w1, entities—namely, tropes—come into and out of existence.

1 comment:

Michael Gonzalez said...

I was under the impression that Presentism means that only present states of affairs are real. "Things existing" is just a subset of that. If the current state of affairs is fully spelled out as "x, y, and z have always existed, and x is in the process of changing from shape a to shape b", the Presentist is happy, and change is just as we naturally imagine it.

I find it incomprehensible that an Eternalist can ever talk of change in w1, since the statement "some entities change in shape over time" on Eternalism just means "some entities are differently shaped 'over there' along the t dimension(s) than 'over here'". Indeed, the 4d shape of an object certainly does not change on Eternalism, does it?

On Presentism, any slice one cares to specify by "w1" is just that world at that particular instant (baseballs floating statically in the air in front of outstretched hands, air compressed statically in front of unmoving open mouths, etc....). If the advantage the Eternalist has is that they can talk about worlds as full 4d unchanging blocks (shaped differently in different static segments of their 4(or more) dimensions), rather than as snapshot slices of an ever-evolving world, then I think the Eternalist has much worse problems with change than the Presentist.