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Italicizing ibid. and idem

Question:

Why is idem italicized while “ibid.” is not? I thought all Latin reference terms had to be italicized.

Answer:

In non-legal writing, the trend is to set all Latin reference terms in roman (i.e. regular) type. The Canadian Style, however, states that “although there is a growing tendency to print Latin reference terms and phrases in roman type (especially when abbreviated), many are still italicized.”

Thus, idem (meaning the same person or thing) is italicized because it is not an abbreviation. Ibid. is a short form for ibidem (in the same place). Because ibid. is an abbreviation, it is written in roman type.

The uncertainty surrounding the use of italics is understandable because in legal writing all Latin reference terms and phrases, including abbreviations, are italicized. To add to this uncertainty, legal writers rarely use ibid. to refer to the cited authority immediately preceding. Instead, they use id., the abbreviation for idem.