As I've mentioned here in other threads, I don't believe that spirit is a substance. In fact I think that thinking of spirit as a kind of stuff is looking in the opposite direction from what might really deserve the name "spiritual". The thing that might well be real, and that would also do the jobs that people mostly want spirit to do, is not an extra simple ingredient that can be added like hot sauce, but rather meaningful pattern that is too complex for humans to perceive clearly.
I'm used to studying the simplest patterns in Nature, involving only a handful of particles doing a few different things, or else large masses of identical particles all doing the same few things. Even within physics one notices an alarming meta-pattern, however. On the one hand, when you look more closely at even the simplest things, they turn out not to be so simple after all. And on the other hand, the number of complicated new things that can happen when more pieces come together never seems to end.
Lately I've been trying to learn some more chemistry and even a bit of biology, and that meta-pattern seems to continue with a vengeance. Electrons do their things within atoms, and atoms jostle around in their molecules, and molecules flop around, and sometimes split and rejoin ... and it's all part of a membrane, which is part of a mitochondrion, which is part of a cell, which is part of an organ. The organs and cells and organelles are not made of anything besides the molecules and atoms and electrons, but their collective behaviours are long, involved stories at their own levels.
Perhaps a sufficiently superhuman mind might not even recognize human concepts like "metabolism", or even "reaction", because they would have no trouble following these phenomena in atomic terms, like an orchestral conductor brilliant enough to glance at a score and hear each quarter-note. Or perhaps grouping things into blocks, and recognizing distinct levels of story, is just what it means to perceive and understand things, and superhuman minds will still do it as we do, just better.
We humans at any rate---at any rate, some of us---are recognising that our own minds themselves are surely higher-level atomic phenomena, like wind or fire or metabolism, only more complicated. And yet the impression I get from scientific materialists who write for the public about this kind of subject is in one way surprisingly limited. These writers can be clear, even eloquent, about how atoms jumble around, and end up making large, complex molecules, even though the atoms themselves are simply doing their atom-y things without any grand plan. Then those molecules wobble and tumble, and we get complex machines. Yada yada yada, neurons, nets, and the mind.
Then it stops. The human mind is the pinnacle of creation, the ultimate meaningful pattern made up of mindless components. Above us there is nothing but "chance", whatever that word might mean. The greater cosmos is meaningless. Nothing more to see here.
This just seems too convenient. The more plausible explanation to me is that we stop seeing meaningful patterns more complex than our own minds, not because those patterns don't exist, but just because our minds cannot hold them. We are like mitochondria diligently recombining ATP molecules without any notion that we are part of a cell, let alone of a brain.
Perhaps sometimes we get a bit of a glimpse of a bigger story. Or perhaps we only think we do. Getting some inkling of something bigger than we are seems possible, though; perhaps not even just the guess that there is something bigger, but some more specific glimpse of what that bigger something is like, expressed in dumbed-down terms we can grasp, like a dog forming a dim, doggy concept, probably about food, of what it means to be part of a human family.
Experiences like that would seem to me to play the role that people seem to assign to things they call "spiritual experiences". And I think that glimpses of a superhuman pattern, even just as a hypothetical possibility, are an important enough concept to warrant a name. So I'm inclined to adopt the existing term "spiritual" for them. Perhaps this risks confusion; but I'd be willing to argue that this is what people have actually meant by "spiritual" all along, whether they knew it or not.
In her song "One more colour", Jane Siberry wrote:I've seen this thing you won't believe.
Why it's big, bigger than the biggest trees:
High as the mountains, wide as the widest skies,
And that's both sides. Well, at least as big as me.
I was a teenager before it was cool.