Some experts reserve the diagnosis of dyslexia or learning disability to those who have, say, some twelve or fifteen traits out of a list of some thirty-five indicators. 1 Others will find alternative definitions and points of demarcation useful. But such criteria, which may be so important in legal and administrative determinations, are, for our purposes, relatively unimportant and can be quite misleading. We may hesitate to apply the term "dyslexic" or even "learning disabled" to someone with only one or two or three of these traits, especially if they are present only in mild form. Yet these same traits may be tremendously important in a given individual case when they contribute in a significant way, positively or negatively, to a person's major abilities or accomplishments.
Thus, certain persons may not have trouble reading or speaking or even calculating, but we would find it of great interest if they had major difficulty remembering numbers or dates, especially if they were well known as mathematicians, and more so if they used special mental dexterity (in certain related but different areas) to devise ways of dealing with the problem. Such a case is that of the quiet Oxford don and lecturer in mathematics, the Rev. C. L. Dodgson, better known as Lewis Carroll.
In the biographical memoir prepared by Dodgson's nephew, Dodgson