# Really dumb question: why do we use e_i for unit vectors?

## Main Question or Discussion Point

Anybody know the history of why something like $$\mathbf{e}_i$$ is conventionally used for unit vectors (as opposed to u for Unit which is less common).

I assume this originates from another language? If so I'm curious what language and what word.

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D H
Staff Emeritus
German, I suspect - ein.

Ah. One (unit). Thanks!

I'd always been told it was short for "element."

HallsofIvy
Homework Helper
I'd always been told it was short for "element."
Never believe what a math teacher tells you!

German, I suspect - ein.
I agree, "e" for "Einheitsvektor" meaning unit vector.

Might also be derived from Euclidean though..who knows for sure..

D H
Staff Emeritus
How come?
He's a math teacher trying to revive Epimenides paradox. Follow his advice: Don't believe anything he says.

I am assuming he is implying with this, that we, students, must check everything out on our own, no matter who tells us that sth is true or not. We have to verify everything on our own, right, is this what halls is saying, right?

Ok, i am gonna check the meaning of that paradox on wiki.

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aaahhh i know that from the "SAT" exam

those logic questions took a decade from my life

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I actually found this discussion to be fairly informative. I never think that asking for historical reasons for notation is a stupid question.

I should have labelled the post "non-technical question: ..." ;)

mathwonk
Homework Helper