In a scientific theory, the definitions are generated by the model and, as such, can't be compared to the descriptive definitions from present psychiatry. However, as in the common language we meet these two terms, as we do not want to invent new terms, they have been kept, but with the definitions as generated by MDT. The general theory does not define, in fact, the diseases. It defines only status and parameters. A status is considered pathological, if some parameters have values beyond certain limits, more or less conventionally imposed. Example: In MDT, the schizophrenia parameter of a normal brain occurs at any time having a different value. The value can be lower (better) or higher (worse), at different moments. Sometimes this parameter can reach the limit considered pathological, even if the person is not sick. The illness is declared if this parameter is permanently and significantly in the pathological zone. We'll describe and then, define the two fundamental illnesses, as they appear in MDT. Schizophrenia The characteristics from lighter to severe cases are: XS1: not enough long-range models exist in order to understand the external reality. The individuals interact normally with external reality, but the context to understand the primary facts is missing sometimes (missing long- range predictions). These individuals succesfully integrate in society, not by all means in unfavoured positions (on the contrary, as we will see later). XS2: Bad understanding of what is going on in front of their eyes, due to the fact that the necessary models are poor quality or inadequate. The capacity to build and operate short-range models is maintained. These individuals are mostly able to be integrated in society, if they have a model of interest for the society. XS3: The person has no adequate long-range model for the external reality, short-range models are scarce. Example: The person does not know where he/she is, even if in his/her own room. Such a person uses only very low quality models, most of them being components of PSM. The chances of integration in society are very limited. On static analysis, XS1 is situated in the non-pathological zone, XS2 is on the border, and XS3 is pathological. The schizophrenia parameter is variable in time. A normal person can be temporarily in XS2 status, and if drunk, sedated or tired, even in XS3, without being declared pathologically schizophrenic. We'll analyze XS1 in detail; two situations can occur: