The theory of the mechanism of AP presented here is summarized as follows' (1) It is possible for many non possessors of AP to acquire a frequency anchor at any age. The ease of acquisition probably depends on prior musical experience and present relative pitch ability, as shown by the striking difference in initial abilities of the different sub jects. Cuddy (1968) also concluded that past experience is important in judging pitch. (2) As with many skills, the younger it is learned, the better. Beyond childhood, any improvement in ear training is apparently hard earned; with only a few sessions, subjects achieved little improvement in pitch identification ability, and months of sessions were re'- quired by myself. (3) There does not appear to be a difference in recognition of individual tones in both performance and verbal reports of possessors of AP and non possessors, once the latter have established a tonic scale tone as an anchor. (4) There do appear to be two basic ways of perceiving music, and the choice is made at a very early age, perhaps infancy. (5) If the choice is made in favor of a single fixed scale, then exposure to music strengthens memory of notes. If, as is more common, the scale "moves," then exposure to music trains one to ignore AP. Thus, AP is trained out of most people. I therefore regard AP as having two different facets. The first, memorization of one or more anchor tones, can occur at any age. The second, regarding musical perception, must probably be determined in early child hood, and coincides with the acquisition or non acquisition of AP at that time. The concept of two mechanisms of musical perception may seem unlikely, but using it, many pieces of the pitch perception puzzle fall into place