Each of these two Models has its own lexicon or terminology. And indeed some words are used in both Models, but with different meanings in the two Models. (And lack of awareness of this contributes to the problems we are considering.)

And probably most (though not all, as we shall see) beliefs within the Objective Model will be able to be found to be a part of one of these two Models, so that we could say that the Objective Model to a great extent consists of these two (sub‑)Models.

These two models that are (sub‑)Models within the Objective Model will be called, in this presentation, the "Physical Model" and the "Mental Model."

(Again, they are both capitalized in this presentation for the same reason that "Objective Model" and "Subjective Model" are capitalized. They are both to refer to the total set of such models, or beliefs, as distinguished from more specific ones.)

This distinction is somewhat understood by everyone, and has been referred to vaguely as the difference between the "physical world" and the "mental world."

Remember that by "world" we are meaning everything that exists, consisting of entities and their tendencies to interact. These entities are the material with which we make our models. So the difference between these two sets of models, related to the vague awareness of these two different "worlds," can best be understood by the introduction of a classification of "entities" for the purposes of this discussion. This is a classification of the entities that are the materials out of which are constructed the Physical Model and the Mental Model.

At the beginning of this presentation, I stated that an entity would be anything that a name or noun could be assigned to. In a sense, however, we could assign a name or noun to anything we could possibly think of, or experience, and it would thereby become an entity. On the other hand, we can readily understand that there are important differences among various things that we have names for, such as chairs, companies, thoughts, discussions, relationships, nations, concertos, dimensions, imaginary objects, etc. So it becomes understandable that we could talk about different "kinds" of entities.

As we try to understand the basic issues that this presentation is about, we will have to understand better how we are using all of our terms, including the term, "entity." Also, I don't believe that it is possible simply to say a few words about the topic and then have a satisfactory understanding of these concepts. I believe such understanding will gradually increasingly develop as the presentation proceeds (and probably with a significant amount of necessary re-reading).

We have noted that we can say that we bring some entities "into existence," so to speak, simply by defining words. We can choose a word that currently has no meaning assigned (by anyone so far) and then draw a circle on a wall, and finally assign the word to the area within that circle. Now there is an "entity" where there was none before, an entity brought into existence, and therefore "existing," by definition only. I believe if we look closely at this issue, we can see that we have many, many entities that exist by definition only. We have noted that one way we could attempt to identify such entities would be to ask whether, if an alien from another galaxy came to Earth and did not know any of our languages, that alien on his or her own would ever come across and be able to identify the entity. He or she would undoubtedly find chairs and houses, but would he or she find North Carolina? Your family? A corporation? Democracy? So some "entities" are brought into existence only because we humans have undergone the first exponential change, the ability to use symbols and the rules of syntax, or language, essentially to an infinite extent.

And let us recognize, even more thoroughly and generally, that something qualifies as an entity only because, so to speak, a line has been drawn around it. If we identify a particular entity as a "door," that entity might consist only of some wood, or it might also include some hinges on it, or even additionally a doorknob, and it might also include the paint (or dirt) on the door or not, this being a matter of arbitrary definition. And we know from modeling developed in modern physics that nowhere "in nature" (the physical world) can it be said that there is a precise boundary up to one side of which there is something that is not on the other side of that boundary also.

So it is we that populate "existence" with "entities," by virtue of our attention being drawn to what we generally call "things," and especially by virtue of our assigning names to those "things" that have attracted our attention. And our attention may even be drawn to some "things" that "exist" only in imagination, or are parts of "things" that "exist" only in imagination.

And to be really thorough, we could look at the problematic word "exists." Let us start with "X exists."

How will this sentence be useful? It might be useful if we are trying to communicate with each other, sharing and comparing our beliefs to see if we agree, so that we can improve our knowledge and our ability to cooperate. But for the sentence to be useful, it will have to have the same meaning to both of us, and therefore we would have to mean the same thing by the same words. Well, we have not yet developed an agreed-upon meaning of "X."

This difficulty could be removed if, for the purposes of this particular discussion either I gave "X" a different label, a word in general usage, and said that it meant what it usually means to people, i.e., its usual definition, or if I gave it my own definition.

But suppose I did one of those two things. Then there is the question as to what "exists" means.

Does it have one meaning that would apply to any word that "X" was replaced by (or any definition I gave of "X")? What can we say we mean about "X" if we say that "it exists"? Is there one thing that we can mean by "exists" that would apply to anything that we meant by "X"?

Try to come up with one answer, using as replacements for "X" the examples already given (North Carolina, your family, a corporation, democracy) and add things like "abstraction," "contradiction," "explanation," "the unimaginable," "the absence of something," "existence," etc.

Is there one meaning that we can give to "exists" that would allow us to arrive at a conclusion with regard to each of those examples as to whether it exists or not? (And what if I said that "X" exists in my imagination only?)

And I don't mean simply to substitute another word or phrase for "exists" that is just as problematic, such as "is" (as in saying that "to exist" is "to be").

The closest concept that has the broadest meaning I believe would be something like "My attention is on this 'thing.' And I have some belief about it, that can most easily be conveyed by saying that I believe it exists (or doesn't exist), and from the context you will have to guess what I mean."

We could then work out together an agreed-upon method (set of criteria) that would enable us to decide whether we were in agreement or not, that is, had the same belief or not.

I will assume that you will not be bothered by this complex problem as I continue to use the word "exists" in what follows.

But in this presentation, the use of the word "model" is quite extensive, and I believe it will be helpful now to review certain aspects of the concept. "Model" is a noun, and it therefore refers to an "entity." So if we have the rock, and the dried mud, each of which is a model of the other, how many entities do we have? There is the rock, and there is the dried mud. That's two entities. But we also have the model of the rock and the model of the mud. Is that two more entities? How did four entities come into existence? And what does it mean in this case for something to "exist"?

So we remember that some "entities" are "brought into existence" "by definition only." So there are different kinds of entities (and thus different meanings, as we have noted, of "exist"). Certainly entities that are brought into existence by definition only are secondary entities. And note that all we have to do is destroy one of those original, primary entities, the dried mud, and we will have destroyed three of them, the dried mud, the model of the rock and the model of the dried mud. The "existence" of an entity called a "model" is dependent only upon whether a particular entity that does exist (in another sense) could be used to predict something (whether it is so used or not).

So again, there are different kinds of "existence." The existence of the rock and of the mud is a different kind of existence than the existence of a "state of affairs," namely, that the mud could be used to predict something about the rock. The rock and the mud are primary physical entities, and our considering the mud to be a model of the rock, although it "brings into existence" another physical entity ("model"), does not bring into existence another primary physical entity. A woman and a child would be two primary physical entities. If the woman had given birth to that child, that would not mean that there were four primary physical entities, a woman, a child, a mother, and a daughter.

Now, moving on, since "things" can draw our attention even prior to the attainment of or use of language, and therefore indeed become regarded as "things" or entities, this recognition of entities probably occurs for many animals in addition to humans. Of course we humans are quite creative in our designations of entities, the term "entity" itself being a tool useful for attainment of agreement for the sake of cooperation. And in fact we humans continue to create even more entities by the processes of "abstraction" and of imagination, leading to essentially an infinite number of potential entities.

We will, for the purposes of this discussion, divide entities into three classes:

(1) Primary physical entities: entities that everyone can "see."

(2) Primary mental entities: entities that only one person can "see."

(3) Secondary entities: entities that no one can "see."

(The word "see" is a simplified term for "experience." Because of its importance for us humans, when we talk about experiencing things, we tend to think primarily of the visual sphere. But we must realize that we are really talking about all sensory modalities, all emotional states, and anything else that we can "notice" or "focus attention upon.")

Within your subjective experience, that which you are specifically experiencing at any given moment, there are two kinds of entities, both of them being "primary," as the term is being used here. There are primary physical entities, all those things that you can experience and point to or make reference to in some way such that others will agree with you, on the basis of their own subjective experience, that the entity is actually "there" (like that chair over there), and there are primary mental entities, all those things that you can experience that anyone else would have to take your word for (like your thoughts, feelings, perceptions, motivations, etc.).

If indeed the difference between primary physical entities and primary mental entities is the ability to point to physical entities and the inability to point to mental entities, then the concept of "pointing" is a crucial one, so we need to look closer at this concept. Just what is this activity called "pointing"?

We have already covered the fact that all you ever have to deal with is your subjective experience. Within that subjective experience are also the manifestations of your beliefs about that subjective experience when those beliefs become active. (Those manifestations may include how you feel and/or what you find yourself doing and/or what images come to mind and/or what words and statements you find coming to mind.) These additional manifestations are simply more of your subjective experience. It is all just your subjective experience.

So you have the subjective experience, for example, of an object in front of you (in your vision), or a particular sound, or a particular smell. There is also another object, a person, standing there in your subjective experience. Now you can do an experiment involving the person. You can in some way, either by gesture or by words, ask the person whether he or she is "experiencing the same thing." We would say that you are calling to the person's attention what you are paying attention to, another way of saying that you are pointing to a thing. And the experiment would result in two possible outcomes. The person might say that he or she indeed was experiencing the same thing, or he or she might ask you what in the world you were talking about. If he or she said that he or she was indeed experiencing the same thing, he or she would be agreeing with you. (That person would be reporting the belief that he or she was experiencing the same thing as you, confirming that you and the other person have the same belief that the thing is "there.") So once again, please note, we come back to the crucial concept of agreement.

So you could perform this same experiment with regard to entity after entity within your subjective experience, and classify those entities according to whether pointing to them resulted in agreement regarding the other person's experience of them or lack thereof.

And during the course of doing so, you might point to a ringing sound, and get a negative response, indicating you are experiencing something the other person cannot experience, most likely an example of tinnitus ("ringing in the ears"). Conceivably, you also might find that you were most likely experiencing some hallucinations, right along with your experiencing of most things that, when pointed to, resulted in agreement. And you could take any such item and describe it further, using words, to indicate what your experiencing of the entity was like, and see if the other agreed. You would be "pointing to" some of the entity's attributes and getting confirmation (or disagreement) regarding those attributes.

But now let's take something that you can point to, say a chair, and can get agreement from the other person that the other person has that chair in his or her subjective experience. You don't know that the other person is being accurate, because you can't experience the other person's subjective experience. So all that is happening is that you (and the other person) are assigning that entity to a category of entities, namely, "physical entities" (or "mental entities"), based upon your experiment. And, of course, you do indeed automatically assign entities to these two categories (physical and mental entities, though not necessarily using that terminology) based upon your ongoing, everyday experience involving interactions with other people (within your subjective experience). You know, from experience, whether other people can perceive your thoughts and emotions without you giving them any evidence, such as emotional behavior or verbal expression, just as you know, from experience, whether other people can also perceive certain things, such as chairs, that you can perceive around you.

We need to recognize that it could also happen that someone else could point to a sound, or other entity, whereupon you would find yourself puzzled, because you were not having that same experience. Under those circumstances, you might wonder whether the other person was "imagining something," or whether you were, for some reason, unable to experience something that was "actually there." This could result in further experiments, but the experiment carrying the greatest weight would be to involve a third person (or more), to see if there was agreement with the other person or with yourself regarding whether the entity could be experienced. If the other(s) agreed that it was indeed "there," you would consider the entity a physical one that for some reason you could not experience. If the other(s) agreed with you, then you would consider the entity to be a mental one, existing "only in the other person's mind." Once again, the concept of agreement as the crucial factor enabling the classification of entities into "physical" ones and "mental" ones becomes evident.

Note that the other person may agree that he or she has the same reaction to something, but that reaction is not what we are talking about. Others can do something to cause themselves to experience something within their own subjective experience that they assume is like what you are experiencing in your subjective experience, but that is not the same thing as experiencing your own subjective experience within their own subjective experience. You may feel sad about something, and so may the other person, but what the other person is experiencing is an entity in that person's subjective experience, not in yours (and vice versa). His or her (reported) sadness is not the same thing as your (experienced) sadness.

This distinction between experiencing the same thing and experiencing a similar thing is similar to the difference between two people looking at and experiencing the same chair in their own subjective experience as compared to two people trying to imagine the chair from a description of it. There is an assumption that what each person is imagining from the description could easily be rather different, such that their imaginations of the chair are obviously two different things, whereas what each person is experiencing when both individuals are looking at the chair is the same except as can be explained by such things as difference in perspective, perceptual limitations, etc., so that they could be said to be seeing the same thing.

So pointing to a primary physical entity is completely different than what might be called pointing to a primary mental entity, as the terms are being used here.

If we both point to a chair and ask each other questions about it, we are assuming that we are pointing to the same thing and experiencing the same thing (though of course our ways of experiencing it, perspective and sensory quality, may be different). The "it" that we are experiencing is, we agree, the same thing, a single entity that we are both experiencing.

The only primary mental entity that I can experience is one within my own subjective experience. No one else can experience that entity. We can talk about it, of course, but not both experience it (even from different perspectives). The best I can do is say, "Look, I know that you must be feeling the same way I am about this, namely (e.g.) anger. So that's what I am talking about. We are both experiencing the same thing." But we aren't both experiencing the same thing, or entity. I am experiencing my anger. You are experiencing your anger. We are not both experiencing one entity. We are each experiencing a separate entity. You have to take my word for it that I am experiencing something "like" what you are experiencing, and there is really no way to know that the experience is similar, even if the label being used is the same. And even if it were similar, it would still be two different experiences, e.g., two different angers, yours and mine, and thus two different entities, not just one.

The act of pointing can actually be considered a part of an act of measurement. Successful "pointing" is a simple form of measurement, involving agreement, and can be accomplished only with physical entities, not mental ones. If I point to something and ask you a question about it, and the answer you give is the same as my answer to that question, or can be linguistically converted into the same as my answer, then the result of the measurement is the same, such as, most simply, a "yes" or "no." "Are we seeing the same thing? For instance, is what you are seeing round and blue?" "Yes. How about you?" "Yes." So each person is saying the equivalent of, e.g., "What I am seeing is round and blue." As such, each person's statement is an act of agreement, reporting similarity of belief, that belief being that what is being seen is so, another example of the merging of "perception" and "belief about that perception." And the reproducibility of the agreement with regard to the results of the procedure of "looking" is consistent with the concept of successful measurement.

So, once again, your subjective experience can be divided up by you into those entities that you can point successfully to (and even measure) and those entities that you can't, the criterion of success being agreement. And that is the crucial difference between "primary physical entities" and "primary mental entities."

The Physical Model as used here is essentially all of the beliefs that the members of our species have developed about primary physical entities. They are our beliefs about chairs, and stars, and chemicals, and sounds certain things make, and lakes, and living organisms, etc. These beliefs, of course, include ones about the ultimate nature of those entities and the rules of the universe that those entities seem to follow, if they do. Therefore, as we have tried to model with increasing accuracy these things that we can all "see," and even "point to," we have used models involving secondary entities, entities that we can't "see" (e.g., atoms, electrons, force fields, electromagnetic waves, etc.), and even entities that we can't imagine (that is, ones that do not resemble anything in our subjective experience, such as black holes, 11-dimensional space, superstrings, etc.), other than as mathematical equations having to do with the results of measurements, and perhaps some of the graphs (on paper or screens) of those equations.

It seems appropriate to refer to those secondary entities used to explain primary physical entities as secondary physical entities, and to assume that secondary mental entities, used to explain primary mental entities, will be different than the secondary physical entities.

Thus, the Physical Model consists of beliefs about primary physical entities and about the secondary physical entities used to explain (model) them.

And the Mental Model consists of beliefs about primary mental entities and about the secondary mental entities used to explain (model) them.

A requirement of the Physical Model, beliefs about the "physical world," as used within the sciences, is that it be completely consistent, that is, non-contradictory. (Science, as discussed above, is distinguished from other methods of attaining beliefs by its strong commitment to adherence to the rules of logic and the rules of evidence for the legitimization of belief. The rules of logic are used to prevent the acceptance of models containing contradictory beliefs.) Therefore the Physical Model (as existing in our species) is obviously not yet complete, because this requirement has not yet been met, as has been discussed above.

On the other hand, we all use the Physical Model, whether educated regarding the sciences or not, and most of us ignore or consider irrelevant the fact that there are within it contradictory beliefs and belief systems, and choose for one reason or another, at a given time, to accept specific beliefs as "probably true" or "true beyond a reasonable doubt" or "true enough" or "true for all practical purposes," or "true enough for the purpose at hand." (Most of us recognize that there are probably many things we ourselves believe that are actually incorrect, even though we do not yet know what those incorrect beliefs are, and may never know.)

The Mental Model, in turn, consists of our beliefs about thoughts, feelings, memories, fantasies, wishes, fears, goals, purposes, imagination, etc. These beliefs, of course, also include ones about the ultimate nature of those entities, and therefore about other presumed entities (secondary mental entities) that are not within subjective experience, such as "subliminal perception," "unconscious anger," and "repressed memories." Any of the primary mental entities can either be observed by you and no one else, or by someone else (one other person) but not you or anyone else. The secondary mental entities cannot even be experienced by you. They can be modeled (e.g., linguistically or with metaphoric images, diagrams, etc.), but not experienced, by anyone.

And all of the things we have said (in the paragraph before the last one) about the Physical Model regarding its uses within the sciences and also generally by everyone, whether educated in the sciences or not, can be said about the Mental Model also.

To review, everyone has "equal access" to primary entities in the Physical Model. A house can be observed by "everyone" (you and anyone else who has such ability to observe and is in the right situation). But that is not true of a feeling or thought, a primary mental entity, to which there is "unequal access," namely, by one person only.

So, again, we can all point to a chair, a star, a specimen under the microscope, a cloud, the ocean, a plant, an animal, a human, etc. These things collectively are the starting point or basis of the development of the Physical Model, and everyone has equal access to them and can point to them, including measuring them, obtaining agreement that what is being talked about is the same thing. But we can never point to a feeling, a thought, a fantasy, a memory, a decision, an imagination, a perception, a sensation, etc., which are the starting point or basis of the development of the Mental Model, as the term is being used in this presentation. You have these things as a part of your subjective experience, but you can't point to them (i.e., your own experiences) in others' subjective experience, nor can anyone point to yours (i.e., cause others to experience your experience within their own subjective experience).

When we model "Subjective Reality" within the Subjective Model, everything that exists is as it is or could be experienced, whether experienced or not.

As we develop the Objective Model, we develop a set of beliefs about a group of entities that we agree we are able to experience and point to (agree are actually "there"), and we add entities to the model that none of us can experience but that add to our ability to predict. And this allows us to use measurements of those entities and their interactions, the measurements being experiences that we can point to and fairly precisely agree upon (if the measuring process is satisfactory). And all of these entities we are calling "physical entities," primary ones being the ones we can see and point to while agreeing we are pointing to the same thing, and secondary ones being ones that we add in to make the model more effective in our effort to predict (and thus to explain). This is our development of the Physical Model, our Model of "Objective Reality," to which we refer as "Reality" as we develop our Objective Model.

Then, because we have already learned how to model for others (describe) our own subjective experience, even though we cannot point to the entities we are talking about, we can use those subjective experiences and words to construct a model of entities and their interactions that seem to "correlate" somewhat with some of the entities and interactions within the Physical Model, and in this way come up with another Model, the Mental Model.