You both seem, at least to me, unable to separate existence from the subjective experiencing of existence. A rock out in space does not require any “subjectivity”, any experiencing, in order for that rock to exist and to be what which it is. Most of the universe is like this, just non-conscious non-subjective and non-experiencing ‘dead matter’.
Matter is simply trapped energy. A particle is a little region of space that has a quantity of energy trapped or stored within it. These are what elementary particles are. When you get to the elements you have these elementary particles grouping together in different ways, producing interesting physical properties such as electromagnetism, things that create chemical bonds. The universe is in the vast vast majority of cases almost entirely made out of the simplest elements.
So what is “consciousness”, or “subjectivity”? What is “experiencing”? Experience comes from having a subjectivity which means to have a perspective from which interpretations usher actively. A rock ‘has a perspective’ because it is a certain thing that is different from things around it, and forces will tend to affect the rock differently than they will affect things near the rock but which are different from the rock, and yet the rock does not have an active perspective, it is not experiencing anything. Forces acting upon the rock do not remain stuck in the rock, they do not trigger dynamics within the rock that go on to change and determine what the rock is and how it acts. That is what happens when forces are exerted upon living things: the force triggers changes in the internal dynamics of the living thing, changes which are categorically different than the force itself, and those changes cascade and process in their own complex causal structures and end up changing the organism itself and its actions.
(And Don, for these purposes here I will agree to use your definition of sentience, namely “has feelings”. Rocks are not sentient because they do not have feelings, and we know this because they lack the structures that we know are what produce what we call feelings. We must also say that sentience is close to, but not required for, experience – it is possible for something to be having an experience but not having any feelings, although that is not typically how we experience.)
If subjectivity is having an active perspective capable of being changed by what is changing around us, and capable of changing us, then this is what it means to have an experience. Therefore this is the basis of what is called phenomenology in philosophy. Since phenomenology is the study of experience, you can’t have phenomenology unless something is experiencing and unless those experiences actually mean something.
Ontology is superior to (prior to, more fundamental than) phenomenology in the sense that phenomenology arises from ontology; phenomenology is a derivation of ontology. Ontology describes what is, phenomenology describes what is experience.
So when you conflate memory (an integral aspect of what it means to experience) with ontology, as I said you are doing and which is what you do when you posit phenomenology in a vacuum (without a corresponding and more fundamental ontological structure), you actually make it impossible to even do phenomenology at all, let alone ontology, because you have cut experience off from what experience actually is, namely a derivation of the ontological.
Edit: Don, just to let you know, you did inspire me to take a look at Dennett. I have found a couple of interesting things in one of his books so far, I will try to work them in here at some point if it seems relevant. I have to say that so far at least he is probably the best (most rational and accurate) contemporary academic philosopher that I know of.