I think it is demonstrably true that the ultimate constituents of reality are simple, immaterial objects. Furthermore, we ourselves are objects of such a kind.

Here is the first argument:

Argument A:

A1. If all actual events are caused by other events, then there is an actual infinity of events
A2. There is not an actual infinity of events
A3. Therefore not all actual events are caused by other events
A4. Any actual event is either caused by another event (event-causation), or it is caused by an object that has not itself been caused to do the causing ('substance-causation').
A5. Therefore, some actual events are caused by objects that have not themselves been caused to do the causing

Here is the second argument:

Argument B

B1. If all existent objects are complex, then there will be an actual infinity of objects
B2. There is no actual infinity of objects
B3. Therefore some existent objects are not complex (that is, some existent objects are simple)

Here is the third argument:

Argument C


C1. If an existent object is simple, then it has not been caused to exist (for there is nothing more basic from which it could be constructed)
C2. There are some existent simple objects (see argument B above)
C3. Therefore, the simple objects that exist have not been caused to exist
C4. All existent objects have either been caused to exist, or exist by their own nature
C5. Therefore, the simple objects that exist, have not been caused to exist

Here is the fourth argument:

Argument D

D1. If an object is material (extended in space), then it is divisible
D2. Simple objects are indivisible
D3. Therefore, the simple objects that exist are not material objects

Clearly the objects that are ultimately responsible for all the events that occur - the objects described in A5 - will be objects that have not been caused to exist, for otherwise the causes of their existence will themselves have been caused to exist (which will once more create an actual infinity of objects or causes). So, the objects described in A5 will be among the objects described in B3 (which are also the objects described in C5 and D3). That is, the objects that are ultimately responsible for all the events that occur are simple, uncreated, immaterial objects.

We ourselves appear to be objects of precisely this kind, as this argument (and many others) shows:

Argument E.

E1. If an object is indivisible, then it is simple, immaterial and has not been caused to exist
E2. My mind is indivisible.
E3. Therefore, my mind is a simple, immaterial object that has not been caused to exist

It does not follow from this that 'we' are the ultimate causes of every event that occurs, or even that the ultimate causes of all events are minds (for though all minds appear to be simple things, it does not follow that all simple things are minds). But it does mean that we have, in ourselves, an example of the kind of things that are, in fact, responsible for every event that occurs.

Anyway, at the moment each of those arguments appears to be both valid and sound, for in each case the premises seem better supported by reason than their opposites.