Honesty about perfect writing
I think honesty from the outset about the quality of writing is important. Clients sometimes ask for their manuscript to be edited to be perfect, but quality in writing has a subjective component. We can improve it but perfection is an elusive aim.
Every writer decides at some point that a piece of writing is finished and ready. However, they know that if they leave their document for a while, then go back to it and read it again, they are likely to tweak and improve what they have written – to improve the clarity or the pace of the story or the way the words are used. Redrafting and editing are all iterative processes; many writers produce multiple versions before they feel that their work is complete. What writers aim for and what readers seek is good writing but it is difficult to pin down exactly what that is.
Perfection v. improvement
Editorial professionals, be they copy-editors or proofreaders, work to improve the content they are presented with. Ask a dozen copy-editors to work on the same manuscript and give them all the same reference books (such as Butcher’s Copy-editing, The New Oxford Dictionary for Writers and Editors, New Hart’s Rules or Merriam-Webster and The Chicago Manual of Style), then read the twelve edited versions. You will find that no two versions will be exactly the same. Why is this?
They will have spotted a great many of the same changes needed in spelling, grammar, capitalization, consistency and the use of language. But their individual suggestions will differ, if only slightly, and across the manuscript there will be a number of variations. Each edited version will be an improvement but no two versions will be the same improvement.
As an editorial professional I aim at perfection, but writing is subjective and each revision of a text will find further improvements to make. There are constraints on everything and deadlines need to be met so, at some point, the work must stop and the improvements deemed sufficient.
Realistically, perfection is the aim and improvement is the reality.