Life
Reinhold lays greater emphasis than Kant upon the unity and activity of consciousness. The principle of consciousness tells us that every idea is related both to an object and a subject, and is partly to be distinguished from and partly united to both. Since form cannot produce matter and a subject cannot produce an object, we are forced to assume a thing-in-itself. This is a notion which is self-contradictory if consciousness were to be essentially a relating activity. There is therefore something which must be thought and yet cannot be thought (Høffding, History of Modern Philosophy, Eng. trans., vol. ii.). See

Robert Keil, Wieland und Reinhold (2nd ed., Leipzig, 1890)
J. E. Erdmann, Grundriss der Geschichte der Philosophie (Berlin, 1866)
histories of philosophy by Richard Falckenberg and Wilhelm Windelband. Letters on the Kantian Philosophy
Kant's critical philosophy was not being accepted as the final truth. According to Professor George di Giovanni, of McGill University, Reinhold tried to provide a foundation for Kant's philosophy in order to remedy this situation. Reinhold distinguished two levels of philosophy. The most basic level was the concern with consciousness and the representations that occurred in it. The second, less basic, level, was the concern with the possibility and structure of the known or desired objects.
Kant's important realization was that the possibility of metaphysics can be established. This can be done only by describing what occurs when the mind is conscious of objects. Kant's weakness was in being overly concerned with the objects themselves. He remained at the second, less basic, level of philosophy. He rarely examined what occurred in consciousness, which is the basic level of philosophy. Kant did not provide a phenomenological description of consciousness. Reinhold was convinced that Kant should have identified the fundamental fact of consciousness that was essential in making cognition itself possible.
Reinhold's Essay towards a New Theory of the Human Faculty of Representation is a description of the main parts and attributes of consciousness. In writing this book, Reinhold turned his attention from the moral issues that Kant addressed in the end section of his Critique of Pure Reason to the epistemological concerns of the beginning and middle sections.
Reinhold examined the necessary conditions of representation, such as subject and object, that must exist in order for an object to be consciously present.

General Theory of Representation

• The thing-in-itself necessarily exists, but cannot be known.
  Human knowledge is restricted to appearances only.
  Principle of Consciousness - The thinking subject distinguishes in consciousness the representation from the subject and the object.
  
  
  
  • This is a certain fact of consciousness.
    The subject is the location of the representation.
    The object is anything that is represented as being present to the subject.
    Representation's Material and Form
    
    
    
    • The representation's material ('Stoff') is a given or received manifold of sensation which is unified when it is attributed to a transcendental object. It allows the thinking subject to distinguish a thing-in-itself.
      The representation's form is a spontaneous unifying act which occurs according to the subject's conditions. It allows the thinking subject to distinguish a self-in-itself.
      The self-in-itself and the thing-in-itself must be assumed in order for the thinking subject to be able to make a distinction between consciousness itself and the object of consciousness.
      We can never know anything in itself, that is, as not representation. An object-in-Itself or subject-in-itself does not have matter (sensation) or representational form, so they cannot be known. Only that which is represented can be known
      Consciousness must contain representation.
      
      
      
      • An empirical representation takes its material from a source that is supposed to be external to it.
        A pure representation takes its material by reflecting on consciousness
        A clear and distinct consciousness of an object is an awareness that consciousness itself is a representation in a subject of an external object.
        Special Theory of Cognition
        
        
        
        • Cognition is clear, distinct knowledge that consciousness contains a representation of an object.
          
          
          
          • Cognition is consciousness's awareness that its own content is a subject's representation of an object.