Serial commas
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In Britain and some other less-enlightened countries, the comma is often omitted before an 'and' in a list. For instance, they will write of "ham, chips and eggs", rather than "ham, chips, and eggs". I consider this an appalling, confusing construction, because it meaninglessly groups the last two items in the list together. Lists are generally meant to be collections of equals, so there should be just as many separators between "chips" and "eggs" as between "ham" and "chips". In many cases, omitting the serial comma is ambiguous. Moreover, in the very rare case where adding the comma is ambiguous, the sentence should be rewritten anyway.
Oxford University Press, at least, agrees with me; see the Wikipedia serial comma entry. Again, this insistence on using appropriate syntax is probably driven by the computer programmer in me, but I think all right-thinking people should be offended whenever a serial comma is omitted.
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Reference:
Dr. James A. Bednar. Tips for Academic Writing and Other Formal Writing