All class notions and concepts are formed by taking note only of the general characters of things and associating them with a symbol called “name.” Things themselves, however, do not exist in the nature of these symbols or names or concepts; it is only an aspect of them that is diagrammatically represented by the intellect in the form of concepts. When concepts are united or separated in our thought and language, they consequently represent only an imaginary plane of knowledge, for the things are not as the concepts represent them. Thus when we say “Caitra’s cow,” it is only an imaginary relation for, strictly speaking, no such thing exists as the cow of Caitra. Caitra has no connection in reality with the cow. When we say purusha is of the nature of consciousness, there is the same illusory relation. Now what is here predicated of what? Purusha is consciousness itself, but in predication there must always be a statement of the relation of one to another. Thus it sometimes breaks a concept into two parts and predicates the one of the other, and sometimes predicates the unity of two concepts which are different. Thus its sphere has a wide latitude in all thought-process conducted through language and involves an element of abstraction and construction which is called vikalpa. This represents the faculty by which our concepts are arranged in an analytical or synthetical proposition. It is said to be _śabdajñānānupāti vastuśūnyo vikalpaḥ_, i.e. the knowledge that springs from relating concepts or names, which relating does not actually exist in the objective world as it is represented in propositional forms. Sleep is that mental state which has for its objective substratum the feeling of emptiness. It is called a state or notion of mind, for it is called back on awakening; when we feel that we have slept well our minds are clear, when we have slept badly our minds are listless, wandering and unsteady. For a person who seeks to attain communion or samādhi, these desires of sleep are to be suppressed, like all other desires. Memory is the retaining in the mind of objects perceived when perception occurs by the union of the cittas with external objects, according to the forms of which the cittas are transformed; it retains these perceptions, as impressions or saṃskāras by means of its inherent tamas. These saṃskāras generate memory, when such events occur as can manifest them by virtue of associations.