NEAL ASCHERSON has made a crucial misjudgement in his defence of Casaubon ('The truth about Casaubon', 20 February). The Key to All Mythologies would not have revealed Casaubon's genius, but his limitations. His research was extensive, but disorganised. This is why he is embarrassed by Brooke's inquiries about his filing system and Dorothea's offer to help him. Will Ladislaw's conversation with Dorothea in Rome reveals that Casaubon has ignored crucial work by contemporary German authors, which would make The Key out of date before it was published. Casaubon's failure to utilise the Vatican library productively was not due to Dorothea distracting him - she only offered to assist him with his work - but to his inability to distinguish between material which interested him and that which was relevant. He is more distracted by Naumann's appeal to his vanity, in requesting him to sit as a model for Aquinas, than by his young wife. His last published pamphlet was badly received, and he is eaten up by this, rather than using the criticism constructively. Finally, it is implied that, had he not been made aware of the possible imminence of his death, he would have continued collecting information indefinitely rather than formulate his notebooks and risk the judgement of other scholars by publishing.