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Is there any (even the most subtle) difference between the meaning (or connotation) of that is and i.e.?

I used to be convinced that they were synonyms, until an editor of a scientific journal changed all occurrences of i.e. into that is.

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4 Answers 4

up vote 9 down vote accepted

I use them interchangeably. kiamlaluno sees a distinction I'm not aware of; even in the specific examples he cites, I would use them interchangeably.

The actual term i.e. is an abbreviation of id est in Latin, which literally means "that is". In fact, when I see i.e., I cannot help but say "that is" in my head; this helps me distinguish it from e.g. (exempli gratia, by the way).

If the editor had it changed, it was probably because "that is" is a little clearer, perhaps to non-primarily English speakers.

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+1 because I use them interchangeably too. And I don't say "that is" in my head only; when I read something aloud, I often read "id est" as "that is". To me they mean exactly the same because of the explanation you give. –  Irene Nov 14 '11 at 18:54
    
+1. I agree. I don't see that the Latin abbreviation contributes anything, any more than 'e.g.' for 'for example' does. They are remnants of a more precious age. –  Barrie England Nov 14 '11 at 18:56
    
Editors sometimes replace Latin abbreviations with English translations for the sake of automated translation, too. –  Monica Cellio Nov 14 '11 at 21:02
    
Thanks. So I guess the changes were due to aesthetic/readability reasons (e.g. to reduce the concentration of punctuation marks, as there were many inline formulas). –  Piotr Migdal Nov 15 '11 at 14:25

That is is used to introduce or follow a clarification, interpretation, or correction of something already said; i.e. is used to add explanatory information or to state something in different words.
The difference is that i.e. doesn't follow a clarification; it is not used for corrections, too.

Those walking boots are synthetic, i.e., not leather or suede.
He was a long-haired kid with freckles. Last time I saw him, that is.
Those are androcentric—that is to say, male-dominated—concepts.

In the second example, you don't write "Last time I saw him, i.e."

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1  
'Those walking boots are synthetic, that is, not leather or suede' means exactly the same to me as 'Those walking boots are synthetic, i.e., not leather or suede.' –  Barrie England Nov 14 '11 at 18:46
    
I didn't say that in the first example you could not replace i.e. with that is. –  kiamlaluno Nov 14 '11 at 19:08
2  
The second example is an unusual idiomatic usage that doesn't relate to any others. The trailing ",that is" meaning "in the very specific context just given" probably arose from loose association with the more normal "to put it another way" meaning. –  FumbleFingers Nov 14 '11 at 20:41

Although the meaning is the same, it would not surprise me to find that in the pre-Gutenberg days when the scribes wrote everything out manually and when Latin was the lingua franca of the literate classes, that saving those couple of characters was considered worthwhile. (Not to mention the gallons of ink saved "by simply not dotting the i's")

What goes around comes around - we now skip, trim and save characters wnevr we cn whn txtng, and "i.e." still has utility.

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although whn txtng u dnt typ d periods n i.e :P –  Pranav Hosangadi Nov 15 '11 at 5:38

"i.e." is the Latin abbreviation for "id est" and is often used in place of the English translation "that is". However, in formal written English it is more appropriate not to use abbreviations. The same applies for the use of "for example" rather than "e.g.".

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