Exercise: Verify yourself and others on the existence and status of the model, which generated any stated truth.
It is known from the general theory that a basic problem in the construction of a model associated to the external reality is that we do not know beforehand the elements of the specific external reality. These elements need to be discovered, and the discovered elements are the only ones we can operate with.
Warning: The external reality, as defined in MDT, can't have elements and relationships. The elements and relations appear only in the model associated to the external reality. However, in many statements we will use notions like elements and relationships of the external reality, but these need to be understood as elements and relations of the model associated to the external reality. For the external reality, one can use the term 'entity', which identified by the model will become an element of it. However, we have no word available to associate to external reality in the case of relations. By perfectioning the language, such deficiencies will be solved.
A basic requirement for the existence of communication is the existence of a single common model accepted by both parts who want to communicate. Without a common symbolic model, there is no communication, as both sides will have their own list of definition of the terms associated to the words.
Usually, communication is done only on symbolic models. However, there are more primitive forms of communication using image models (between people, between humans and animals, between animals).
The reality is defined in the general theory as the sum of all truths generated, or possibly generated, by a model. As each person has his/her own collection of models, the reality as understood by each person is different from one person to another.
It is important to specify that in the domain of positive sciences, fundamental models generally accepted do exist. One of these models is e.g. Newton's Mechanics. As this model generates a reality, all physicists consider that the 'reality' is the one generated by Newton's Mechanics, within its limits of applicability.
Due to reasons associated to confusions of the science of knowledge, the reality generated by Newton's model is considered as 'objective'. Thus, "objective reality" is a term generated by a generally accepted model in specified conditions. From this point of view, the fact that the Sun revolves around the Earth is an "objective truth", at least at the level of the year 1500.
It needs to be stated by all means that without a model, the external reality cannot be perceived. After building a model associated to the external reality, what we perceive is what the model states as perception. If, e.g. we say that 'snow is white', this is the result generated by a model associated with external reality, external reality which contains the element 'snow'. One of the properties of the element 'snow' is that it is white. Under the microscope (another model) the same snow looks transparent.
As we already mentioned, reality is the one generated by the model associated to a given external reality. Each time we state a truth, we have to specify first the model.