My general position on the nature of reality is empirical realism.

That is to say, I hold that there definitely is an objective reality, as opposed to any kind of relativism, idealism, or nihilism, which hold either that what is real is relative to some group's beliefs or to someone's subjective experiences, or else (as I consider equivalent to those) that nothing is actually real at all.

But I also hold that the content of that reality is entirely empirical in nature, that there is nothing real that is in principle beyond all observation, that if something exists, there will be some noticeable difference in the reality that we experience compared to what we would experience if it did not exist, and the whole of that thing's existence is the observable differences in reality it makes.

This empirical realism might well also be called physicalist phenomenalism, in that it holds that only physical phenomena exist — which is to say, things that are observable (phenomena) in an objective (physical) way accessible to all observers and not mere figments of any one person's imagination. This kind of view traces back to at least John Stuart Mill, who held the "permanent possibilities of experience" to constitute the entirety of an object's existence.

This is a kind of monism, holding that there is one kind of stuff that exists that all the many things in reality are made up of, in contrast with pluralist ontologies that hold that there are multiple fundamentally different kinds of stuff, especially with dualism as espoused by the likes of Rene Descartes which holds that there are wholly different mental and physical kinds of stuff. It is not quite the usual monism held contrary to that dualism, namely materialism, though as described above it is definitely physicalist; nor is it quite the other usual kind of monism, idealism, though as described above it is definitely phenomenalist.

But neither is it quite neutral monism in the usual sense, as espoused by the likes of Baruch Spinoza, as that holds that there is one kind of stuff that has both mental and material properties; whereas I hold that there are not so much different kinds of properties, much less different kinds of stuff, as there are what could crudely be called mental and material ways of looking at the same properties and the same objects, that are essentially both mind-like and matter-like in different ways, that distinction no longer really properly applying when we really get down to the details.

I would say that the most concrete things that exist are, as Alfred North Whitehead called them, "occasions of experience". These are the things of which we have the most direct, unmediated awareness, and the only things of which we can have no doubt.

Rene Descartes famously attempted to systematically doubt everything he could, including the reliability of experiences of the world, and consequently of the existence of any physical things in particular; which he then took, I think a step too far, as doubting whether anything at all physical existed, but I will return to that in a moment. He found that the only thing he could not possibly doubt was the occurrence of his own doubting, and consequently, his own existence as some kind of thinking thing that is capable of doubting.

But other philosophers such as Pierre Gassendi and Georg Lichtenberg have in the years since argued, as I agree, that the existence of oneself is not strictly warranted by the kind of systemic doubt Descartes engaged in; instead, all that is truly indubitable is that thinking occurs, or at least, that some kind of cognitive or mental activity occurs. I prefer to use the word "thought" in a more narrow sense than merely any mental activity, so what I would say is all that survives such a Cartesian attempt at universal doubt is experience: one cannot doubt that an experience of doubt is being had, and so that some kind of experience is being had.

But I then say that the concept of an experience is inherently a relational one: someone has an experience of something. An experience being had by nobody is an experience not being had at all, and an experience being had of nothing is again an experience not being had at all. This indubitable experience thus immediately gives justification to the notion of both a self, which is whoever the someone having the experience is, and also a world, which is whatever the something being experienced is.

One may yet have no idea what the nature of oneself or the world is, in any detail at all, but one can no more doubt that oneself exists to have an experience than that experience is happening, and more still than that, one cannot doubt that something is being experienced, and whatever that something is, in its entirety, that is what one calls the world. So from the moment we are aware of any experience at all, we can conclude that there is some world or another being experienced, and we can then attend to the particulars of those experiences to suss out the particular nature of that world.

The particular occasions of experience are thus the most fundamentally concrete parts of the world, and everything else that we postulate the existence of, including things as elementary as matter, is some abstraction that's only real inasmuch as postulating its existence helps explain the particular occasions of experience that we have.

George Berkeley famously said that "to be is to be perceived", and I don't agree with that entirely, in part because I take perception to be a narrower concept than experience in a broader sense, and because I don't think it is the actual act of being experienced per se that constitutes something's existence, but rather the potential to be experienced. I would instead say not that to be is to be perceived, or that to be is to be experienced, but that to be is to be experienceable.

And I find this adage to combine in very interesting ways with two other famous philosophical adages: Socrates said that "to do is to be", meaning that anything that does something necessarily exists; and more poignantly, Jean-Paul Sartre said that "to be is to do", meaning that what something is is defined by what that something does. Being, existence, can be reduced to the potential for or habit of some set of behaviors: things are, or at least are defined by, what they do, or at least what they tend to do. (Coupled with the association of mass to substance and energy to causation, this notion that to be is to do seems to me a vague predecessor to the notion of mass-energy equivalence).

To combine this with my adaptation of Berkeley's adage, we get concepts like "to do is to be experienced", "to be experienced is to do", "to be done unto is to experience", and "to experience is to be done unto".

This paints experience and behavior as two sides of the same coin, opposite perspectives on the same one thing: an interaction. Our experience of a thing is that thing's behavior upon us. An object is red inasmuch as it appears red, and it appears red inasmuch as it emits light toward us in certain frequencies and not others: the emission of the right frequencies of light, a behavior in a very broad sense, constitutes the property of redness. Every other property of an object is likewise defined by what it does, perhaps in response to something that we must do first: an object's color may be relative to what frequencies of light we shine on it (e.g. something that is red under white light may be black under blue light), the shape of the object as felt by touch is defined by where it pushes back on our nerves when we press them into it, and many other more subtle properties of things discovered by experiments are defined by what that thing does when we do something to it.

We can thus define all objects by their function from their experiences to their behaviors: what they do in response to what it done to them. The specifics of that function, a mathematical concept mapping inputs to outputs, defines the abstract object that is held to be responsible for the concrete experiences we have. Every object's behavior upon other objects constitutes an aspect of those other objects' experience, and every object's experience is composed of the behaviors of the rest of the world upon it.

All of reality can then be seen as a web of these interactions, the interactions themselves being the most concrete constituents of that reality, with the vertices of that web constituting the more abstract objects, in the usual sense, of that reality.

We each find ourselves to be one complex object in that web, and the things we have the most direct, unmediated awareness of are those interactions between our own constituent parts, and between ourselves and the nearest other vertices in that web, those interactions constituting our experience of the world, and also our behavior upon the world. By identifying the patterns in those experiences, we can begin to build an idea of what the rest of the world beyond that is like, inferring the existence and function of other nodes beyond the ones we are directly connected to by their influence in the patterns of behavior of (and thus our experience of) those nearest nodes.

This work is where philosophy ends, as far as investigating reality goes at least, and the physical sciences take over, postulating the existence of abstract objects with functions that would give rise to the concrete experiences we have of the world. Early physics began by identifying the behavior of large complex objects, and the different kinds of stuff that they are made of, "elements" like "earth", "water", and "air". But in time it has found those all to be made of many kinds of smaller particles of a similar nature to each other, molecules, interacting with each other in different ways. Those many diverse molecules have in turn been found to all be composed of a more limited set of still smaller particles, atoms; and those in turn of an even smaller set of smaller particles still, electrons and nucleons like protons and neutrons; the latter in turn made up of triplets of two still smaller and more fundamental particles called up and down quarks.

And I believe that contemporary physics has come far enough along, dug deep enough into the constituent particles of reality, that it has now identified as its most fundamental particles objects that are literally identifiable with the very "occasions of experience" that make up the web of reality described in my ontology above.

For clearest illustration, consider the experience of vision, which is now understood to be mediated by particles of light called photons. Whenever we see anything, all we're actually seeing in the most technical sense is the photons that hit our eyes; the objects we see, in the casual sense most people mean, are only inferred from the patterns in those photons hitting our eyes. Because of the distortion of space and time relative to motion, from the frame of reference of any given photon, the distance that it travels between whatever emitted it and your eye is zero, and the journey takes no time at all; from the photon's perspective, it exists only at a point and only for an instant,the whole of its being constituted entirely by the interaction between whatever emitted it and your eye. Contemporary theories of physics hold that fundamentally, all of the most fundamental particles are essentially like photons in that way, all naturally moving at the speed of light, and so finding themselves, in their own frames of reference, to exist for but an instant at the point where two other objects interact, and their own existence consisting entirely of that interaction between them.

It is only the aggregate patterns of interactions between these particles that gives rise to the appearance of the conventional, slower-moving particles out of which all of the aforementioned structures arise, up to the macroscopic scale we're familiar with. For instance, electrons as we commonly understand them are understood to be an aggregate pattern of two different light-like particles, each similar to an electron and to each other but differing from each other in a property called spin, neither of which is able to travel any measurably large distance in space without immediately interacting with something called the Higgs field. The Higgs field absorbs that particle, and immediately emits another identical to it other than having opposite spin, only for that to be immediately reabsorbed and a particle like the first one emitted again, the overall pattern of those two kinds of particles, oscillating between each other immeasurably quickly as they interact with the Higgs field, constituting the particle that we conventionally think of as an electron.

Those light-like fundamental particles, that I think are identifiable with the interactions or "occasions of experience" that constitute the web of reality as described here in my ontology, thus make up, in a sense, the electrons and quarks that make up the atoms that make up the molecules that make up all of the matter that makes up the entire world, including people like you and me.