View that statements about material objects are reducible to statements about actual and possible sensations, or sense-data .
According to phenomenalists, a material object is not a mysterious something "behind" the appearances presented in sensation. If it were, the material world would be unknowable; indeed, the term matter is unintelligible unless it somehow can be defined by reference to sensations. In speaking about a material object, then, reference must be made to a very large system of possible sense-data, only some of which (if any) are ever actualized. Thus the statement "There is a fire in the next room" would be analyzed as a series of hypothetical statements such as "If one were to enter the next room with one's eyes open, one would see a bright light of a yellowish orange colour." Some philosophers have objected that it is difficult to remove all references to material objects from the hypothetical statements to which material-object talk is supposedly reducible. See also George Berkeley .