Following my unwarranted notes on philosophy, Here I write about my understanding of philosophical agents specifically. These agents have two defining properties: the faculties of experience and reason. But structurally all philosophical agents observed so far are atleast living beings. They are alive. This demands us to first understand what it means to be alive then how experience and reason are developed and finally to see how this gets back to "things".
A composite entity is considered alive if it is naturally assembled from chemical components and maintains its distinct organization and functionality through autonomous, continuous interactions with its environment. Specifically, an entity is alive if it can:
It has a definite boundary (physical and functional) that separates it from its environment.
It actively acquires, transforms, and incorporates external resources to replace any decayed or damaged components, thereby preserving its internal structure and operational capacity. This ongoing self-maintenance defines its physical identity.
Even during periods of dormancy, the entity must possess a latent potential to resume its self-sustaining processes when conditions become favorable. If this potential is irreversibly lost (for example, through extensive structural degradation), then the entity is deemed as dead.
While not strictly necessary for the basic definition of life, many living entities also have the capability to reproduce either by generating an independent copy as a whole or through incremental replacement of their components—thus propagating their organizational pattern.
Sentience is the natural ability to percieve and be aware of the existence of the self. This can also be called as conciousness (a problem of jargon). Not every living thing is sentient.
Sentience require the faculties of reason and experience. This equates sentient beings to philosophical agents. From a basic understanding of biology and neuroscience, it is clear that experience requires sensory inputs and neural processing of it. This creates thoughts or mental constructs or ideas. Whatever you choose to call them. The important part is that these thoughts are not necessarily propositions but rather non-verbal model or concepts. If you are just born and see something for the first time, there is no definite language to describe it but only a raw mental model that is built on how the sensory experience gets recorded in you. We can say that all things are mental constructs formed by our mind by combining properties from memories of sensory experiences. For example, the color red is a thing in your head, because it is the result of some sensory experience. The feeling of cold is also a thing. But this device on which you are reading all this is not just a mental contruct but an entity, an ontologically existing thing, something real. But the confidence in you about it being real is contingent on the consistent correspondence of sensory experiences with the mental model you have of your device. We call something to be truly real only if it all the available senses supports its existence. When not, it remains abstract. The brain constantly performs model fitting using sensory input. This mimics the scientific method: hypothesis from instinctive memory → test with reason → update in memory as learning. Consciousness hence can be understood as the continuous flow of mental interpretations and modelling. This creates the ground zero or basis of our creativity, the ability to focus and deduce. Abstract thinking, dreams, and imagination arise from memory-driven reasoning since you need the memory as substrate to operate reasoning on. Focus means filtering sensory and memory noise. This is hard because it goes against the default flow since evolution shaped the brain for survival-efficient reasoning which we have internalised and called as intuition or instincts.
I understand three important aspects here: first is that the definition of things in general is not possible at least for now. All I did was re-establishing the connection between ontologically real entities with mental concepts. This directs to the second aspect that all sentient beings run a raw form of scientific method already in their brains. Finally the third is that whatever really exists beyond the perception (even if aided by technology) of any being, the answer to why anything exists at all or what existence is are problems beyond this mental model framework of sentience.