  This central Machian insight that perception is always relational and constructed lies at the origins of Gestalt Theory. The seminal article of Gestalt Theory, Christian von Ehrenfels’ 1890 “Über Gestaltqualitäten,” begins with a review of these ideas, found in Mach’s 1886 Analysis of Sensations. Sensations are not simply raw experiences, but the interaction of experience with a pre-formed cognitive structure. For instance, when we hear a known melody, we recognize it no matter what key it is played in. It can be hummed, buzzed, or strummed on a guitar. Furthermore, even if one or more notes are incorrect, we still recognize it. Mach asks, “what constitutes a melody?” It seems incorrect to say that the actual sound vibrations constitute the melody as we have just seen that numerous different sounds can make the same melody. But on the other hand, it seems empirically odd to say that a melody is not constituted out of its sounds. The actual melody, then, exists in our ability to recognize it. It is formed by experience of one or more examples of the melody, but it is an idealization of that experience. Significantly, the idealization captures not the actual sounds, but the relationships of the sounds to one another. Thus a melody can be sung in a high or low pitch, etc., but as long as the relationships remain the same we recognize it as the same melody. For Mach, this process is at the basis of all perception. Experience requires an ‘a priori’, but that a priori is itself formed by experience.  This process is also at the root of evolutionary processes.