I was thinking recently about how Leibniz accounted for the phenomenon of time. On an A theory of time, it is easy to account for the phenomenon of one event succeeding another; namely one simply appeals to ontology, because events really do ontologically come into, and go out of, existence. I’ve outlined before that the A theory of time is problematic for a Catholic (in particular because it implies that God can “learn things” in a qualified sense which dissolves the classical Catholic doctrine of God’s Metaphysical Simplicity).
However, on Leibniz’ monadology, time is not ontologically real in the sense that the A theory implies. Instead, monads (which are immaterial atoms of substances, and are the fundamental building blocks of all other things which exist) are nodes of perception. They all perceive other monads according to a monad’s complete concept. If one is not familiar with Leibniz this is going to be a bit much to explain in one post, and I’d recommend reading Leibniz here. I’ve been thinking about Leibniz’ suggestion that the appetitive quality of monads is what explains the arrow of time and the phenomenon of time. Monads not only perceive, but they have appetite, and this causes then to move by their very nature from one state-of-perception to another. I find Leibniz’ system completely fascinating, and if it did not pose such problems theologically as it does I would likely accept it, since it makes so much sense of substantial form, animal perception, and in short solves almost all the paradoxes of metaphysics.
In thinking about it more recently, however, I was wondering about taking this kind of explanation – that the soul has an appetitive quality – and marrying that to some other metaphysical system. Say, for example, something like the Medieval Doctrine of Exemplarism, according to which God is psychologically the first known, and it is ‘in him’ that we see ideas and so forth. Some have wanted to place Nicholas Malebranche, the student of Rene Descartes, in this tradition of Exemplarism with Bonaventure. Whether that’s entirely accurate or not, I’m not sure, but in any case, he gives a succinct quote which I think is useful here to help convey the idea. He says:
We must know, further, that God is very closely united to our souls through his presence, so that we can say that he is the place of minds in the same way that spaces are, in a sense, the place of bodies.
Now, on this model of the human soul’s relation to God, might it not be the case that the human soul has this appetitive quality, and this is plausibly what accounts for the phenomenon of time – the experience of a succession of events? This doesn’t seem immediately problematic, though problems can be imagined. For instance it implies that people in Hell either have no appetite, and therefore never experience anything beyond the single moment (for which some explanation would be wanting) or else that those in Hell have an appetite still and thus experience a sequence of events infinitely, thus having appetite even in a state of damnation. Of course, either of those are actually not problematic, but rather are simply very interesting. One real problem I can imagine is that we’d be stuck saying of animals that whatever perception they have, they do not experience temporal succession consciously anymore than rocks do. I think my intuition is with Leibniz in saying against Descartes that that is a counter-intuitive (in a non-technical sense) conclusion which seems to belittle animals and strip them of their dignity. According to Leibniz’ model, which he argues isn’t very far from Aquinas’, The animal soul is indivisible, and immaterial, and yet is qualitatively different from the human soul – however, in the end, either one is just a monad.
Perhaps one could argue that animals perceive the flow of time just to the extent that all of creation ‘yearns’ and thus has this appetitive quality inherent in it. This may imply something for an evolutionary-model of the ‘Spirit’ which Pope Benedict XVI wrote about, and you can read a little bit about that here. However, I’m really just grabbing at thin air here – I don’t see a better system than Leibniz’ to satisfy this paradox and also satisfy our intuitions. However, I am convinced that his system is wrong, and also that he’s on to something here with reference to appetite as an explanation for the phenomenon of time.
 Malebranche, The Search After Truth, p.207