Particle phonology has evolved from a dissatisfaction that I experienced working within the current theoretical and notational framework of generative phonology. I had been looking at historical processes affecting vowels and diphthongs. In trying to describe the kinds of changes undergone by these entities, I was particularly frustrated by the inability of the standard notation to characterise in any enlightening way the internal structure of vowels, as well as relationships evident between particular vowels and diphthongs. The first difficulty – the nature of the internal structure of vowels – was not simply due to an inadequate set of distinctive features. Rather, the problem resided in the very notion of features as autonomous building blocks out of which segments are composed. This view contributed partially to the other difficulty – the expression of relationships between vowels and diphthongs. An additional factor to this problem came from restrictions of the notation in regard what could appear to the left and to the right of an arrow. The notation forced me to formulate rules whose statements often did not accord with my conception of the nature of the processes. It seems to me that a highly-valued notational system should have the property that I have come to call ‘mirroring’. If one believes that a process or change happens in a certain way, then the notation should not just describe that event but should reflect as closely as possible its manner of occurrence.