Appendix and appendum

Reader’s question: What’s the difference between an appendix and an addendum? Can they be used interchangeably or should we be using one over the other in specific circumstances?

Answer: My first reaction was that these terms are not interchangeable, but when I looked in a dictionary, I was surprised to find that one definition of an addendum was ‘an appendix’. Another definition was ‘an addition’, and that’s how I regard an addendum. I distinguish between these words as follows:

An appendix supplements the body of a document, providing detailed information that not everyone will want to read. Appendices are often statistical, historical or technical.

An addendum is extra information that the writer discovered after writing the report, such as a new study on the topic. It’s a bit like a PS.

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