Am Mon, 21 Mar 2011 10:51:44 +0100 schrieb Cecil Westerhof:

> Until now I always used a - (minus sign) to define a sub sentence or for an
> optional word, like:
>     This is -now- not necessary,
>
> I understood that normally you use the em dash for this. But for only a
> word, this seems a little big. Could I then use an en dash or should I keep
> using a minus sign?

It depends. In germany I would use an en dash and put spaces around
it: dies ist -- noch -- nicht notwendig.

Older english books often use --- without spaces: is---now. But
spaces and endash with spaces are used too:

http://en.wikipedia.org/wiki/Dash#En_dash_versus_em_dash

So check the typography rules of your country/language.