data. Ehrenfels extended these qualities to "Gestalt qualities of a higher order," (such as marriage, service, theft, and war) concepts that retain their identity even though the examples that instantiate them change. For philosophers and psychologists of the 1890s, it was not clear whether these qualities of structure were philosophical or psychological. The Gestalt theorists would attempt to integrate both in an experimental science. Jonathan Crary describes Ehrenfels' assertions within the modern problem of form as the attempt to formulate "laws" that would give to perception a semblance of the same unconditional guarantees that vision had had within the classical regime of visuality. The starting point of the theory of Gestalt qualities was the attempt to answer the question: what is a melody? The evident answer is the sum of the individual tones which make up the melody. The fact that the same melody may be made up of different groups of tones opposes this theory. Ernst Mach, who was struck by this fact, drew from it the conclusion that the essence of melody must reside in a sum of special sensation which accompany the tones as aural sensations. Mach did not know how to specify these special sensations. The pivotal step in founding the theory of Gestalt qualities was the declaration that if memory images of successive tones are present as a simultaneous consciousness-complex, then a presentation of new category can arise in consciousness. This would in turn be a unitary presentation, which is uncharacteristically associated with the presentations of the related complex of tones. Principles of Gestalt All of the above properties of perception – the constant figure, the background – in gestalt is in a relationship with each other and represents a new property. This is the gestalt form quality. The integrity of the perception and its order are achieved through the following principles of Gestalt psychology: Closeness. Nearby incentives tend to be seen together. Similarity. Incentives that are similar in size, shape, color or form tend to be seen together. Integrity. Perception tends to simplicity and integrity. Insularity. Reflects the tendency to complete a figure so that it takes a full form. Contiguity. The incentives’ closeness in space and time. Contiguity can predetermine the perception when one event causes another. Common area. Principles of gestalt form our everyday perception, along with learning and past experiences. Anticipating the thoughts and expectations and actively manage our interpretation of