This paper specifies nothing less than an underlying cause of dyslexia. It is a cause which may be responsible for lacking responsiveness to both the teaching of phoneme awareness and to initial reading instruction. Can a single phonological factor explain many of the phonological deficits related to dyslexia? In this paper it is suggested that the answer may be affirmative and that indistinct phonological representations of lexical items in long term memory may be such a unifying factor. Results are summarised from a correlational study of adults and from a longitudinal and intervention study of at-risk children.