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Latin abbreviations in academic writing — e.g., i.e., et al., ibid.

What each Latin abbreviation actually means, how to punctuate it, and when style guides let you use it — including the e.g./i.e. distinction that reviewers love to mark up.

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The everyday set

Abbrev.	Latin	Means	Usage note
e.g.	exempli gratia	for example	Introduces a NON-exhaustive example list. APA: only inside parentheses; follow with a comma.
i.e.	id est	that is	Restates or makes precise — not for examples. Also comma after, parentheses-only in APA.
et al.	et alii	and others	Citations with 3+ authors. Period after "al." only; no italics; "et al." is plural (use ≥2 remaining authors).
etc.	et cetera	and so on	Avoid in formal prose; never combine with "e.g." (the example list is already non-exhaustive).
cf.	confer	compare	Points to a CONTRASTING source, not a supporting one — "see" is for support.
viz.	videlicet	namely	Introduces a complete, exhaustive specification. Mostly legal/older prose; "namely" is clearer.
vs. / v.	versus	against	"vs." in scientific prose (t-test: treatment vs. control); "v." in legal citations.
ca. / c.	circa	approximately	Uncertain dates and quantities: "ca. 1850", "ca. 40 participants".
N.B.	nota bene	note well	Flags an important caveat; sparingly, mostly in footnotes.

Citation and footnote machinery

Abbrev.	Latin	Means	Usage note
ibid.	ibidem	in the same place	Repeats the immediately preceding footnote’s source. Chicago allows it; APA does not use it at all.
id.	idem	the same (author)	Same author, different work — mostly legal citation.
op. cit.	opere citato	in the work cited	Refers back to an earlier-cited work. Deprecated by most modern styles — repeat a short citation instead.
loc. cit.	loco citato	in the place cited	Same work AND same page as an earlier citation. Also effectively obsolete.
q.v.	quod vide	which see	Cross-reference within your own document/encyclopedia entry.
s.v.	sub verbo	under the word	Citing a dictionary/encyclopedia entry: "OED, s.v. “research”."
et seq.	et sequentes	and following	Page ranges: "pp. 14 et seq." — modern styles prefer explicit ranges.
passim	—	throughout	The point recurs throughout the source rather than on one page. Use sparingly.
[sic]	sic erat scriptum	thus it was written	Inside quotations only: marks an error as the original author’s. Brackets, usually italicized.

Latin phrases used as ordinary vocabulary

Phrase	Means	Usage note
a priori / a posteriori	from reasoning / from observation	A priori power analysis = planned before data. No italics in APA (naturalized).
ad hoc	for this purpose	"Ad hoc analyses" = unplanned; label them as exploratory.
per se	in itself	"The effect is not causal per se" — no italics.
de facto / de jure	in practice / in law	Contrast between actual and official states of affairs.
in situ	in its original place	Measurement without removal or disturbance.
in vivo / in vitro / in silico	in the living / in glass / in silicon	Whole organisms / cell or tube systems / computer simulation. Italicization varies by journal — be consistent.
inter alia	among other things	Formal prose and law; "among others" is plainer.
ipso facto	by the fact itself	"A significant p-value is not ipso facto an important effect."
sensu stricto / lato	in the strict / broad sense	Taxonomy and definitions: which reading of a term you mean.
ceteris paribus	other things equal	Economics: holding all other variables constant.
prima facie	at first appearance	"Prima facie evidence" — before deeper scrutiny.
sui generis	of its own kind	A case that fits no existing category.

Style-guide rules worth knowing

APA 7: use the abbreviations (e.g., i.e., etc., cf., viz., vs.) ONLY inside parentheses; in running text write the English equivalent ("for example," "that is"). Exception: "et al." and "v." in legal references are fine anywhere. None of these common abbreviations are italicized — they are considered naturalized English.

Punctuation traps: "e.g." and "i.e." take a following comma in American English; "et al." has a period only after "al" (it abbreviates "alii", while "et" is a complete word); "etc." absorbs its period at the end of a sentence (never "etc..").

When in doubt, prefer English. Modern style guides (APA, AMA, most Nature journals) treat Latin as a readability cost: "ibid." and "op. cit." have been dropped by APA entirely, and "namely" or "compare" communicates to more readers than "viz." or "cf."

Frequently asked questions

What is the difference between e.g. and i.e.?

"e.g." (exempli gratia) gives examples — some members of a larger set: "nonparametric tests (e.g., Mann–Whitney U)". "i.e." (id est) restates exactly — the full definition: "the control condition (i.e., the waitlist group)". Test: if you could write "for example", use e.g.; if "in other words", use i.e.

When do I use et al. in APA 7?

In-text: works with 3+ authors are "First Author et al." from the FIRST citation (a change from APA 6). In the reference list: spell out up to 20 authors. And "et al." must stand for at least two people — for a two-author work, name both every time.

Should Latin terms be italicized?

Naturalized abbreviations and phrases (e.g., i.e., et al., a priori, per se, in vitro, ad hoc) are set in roman type by APA, Chicago and most science journals. Italics are reserved for genuinely foreign or unusual Latin ("sensu stricto" in some journals), for [sic] by some styles, and for species names — which follow their own binomial rules.

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