i.e. and e.g. are two tiny Latin abbreviations that do opposite jobs, and because both are usually read silently, people swap them without noticing.

i.e. stands for id est, "that is". It promises that what comes next is the same thing again, said more exactly. "The café shuts in winter, i.e. from December to February" doesn't give an example of winter closing; it defines it. Whatever follows i.e. should be complete.

e.g. stands for exempli gratia, literally "for the sake of example". It promises a sample, not the whole set. "Pack something warm, e.g. a fleece or a scarf" leaves the door open to gloves, hats and everything else.

The test is to read each abbreviation aloud as its English meaning. If "that is" or "in other words" fits, you want i.e. If "for example" fits, you want e.g. And because e.g. already signals an incomplete list, adding etc. at the end repeats the point.

Punctuation varies. Dictionary.com advises a comma after each abbreviation (", e.g., "), while Cambridge Dictionary's British examples ("closed during low season, i.e. from October to March") use none. Both conventions are in use; pick one and keep to it.

Memory trick. Read i.e. as "in essence" (here's the whole thing in other words) and e.g. as "example given" (here's one of several). The letters don't stand for those words, but they map onto the right meaning.