Letters to the Editor

This letter is associated with the following article:
They may be invisible and their art unsung. But in the age of blogging, editors are needed more than ever.
  • Questions for Slackie

    or anyone who can answer them.

    I've just started to teach English and get into proofreading/copyediting, and I'm always coming across things that mystify me. I'm genuinely looking for some clarification, so please don't think I'm being snarky or smug.

    Slackie wrote: "It's the difference between a cleanly, clearly communicated idea, and noise."

    Is that last comma, between "idea" and "and," technically allowed to be there? Under what justification?

    And: "Editing's an invisible art, and, sadly, appears to be going by the wayside..."

    Since that's a compound predicate (IS an invisible art and APPEARS to be going...) and not a compound sentence, why is there a comma before the conjunction?

    Thanks so much for your help.