że & iż

I was taught that iż is used in a sentence when że has already appeared so as not to be repetitive. One example:

On uważa, że ojciec już wszystkim mówił, iż pochodzi z Hiszpanii.
(as opposed to)
On uważa, że ojciec już wszsytkim mówił, że pochodzi z Hiszpanii.

Is this an iron-clad rule or simply a question of stylistic preference?

"Iż" is a bit oldfashioned word.
In spoken language it doesn't sound very natural. It is used in books mostly.

Nobody says "iż" nowadays.I always say "że"

In spoken language it's really rarely used but you can still hear this sometimes.In written language it's still in use as you said to avoid repetition.

Does anyone think this sentence sounds bad?

"Iż" is a borrowing from the Czech language and in fact has never been used in spoken language in Polish. Everyone who uses it this way sounds a bit silly (unless he is a politician, but they typically speak as if they were reading a newspaper, so instead of telling you: nie wiem, they will say: nie mam takiej wiedzy, which is unacceptable for a decent newspaper) ... but you can spot "iż" quite often in the press.

Not true. The Czechs use "že" as well. ;-P

It's perfectly OK in speech, but in writing one of the "że"-s would need to be replaced with "iż". It's a matter of good style really. Check in any novel.

Usually the first one remains "że" and the second changes into "iż", but it depends on the sentence, can be the other way around.

Ok, thanks.

I didn't say that the Czechs don't use "že". I said that the "iż" is a borrowing to Polish from Czech.

In order for the Poles to be able to borrow "iż" from Czech, the Czechs would have to use it. They don't, and as far as I know, never did.

BTW obywatel was also borrowed form the Czechs. According to Polish word-forming convention it should have been obywaciel like nauczyciel, przyjaciel, etc.

Obywaciel would sound great (although a bit silly after all); we're so accustomed to it in Polish that I'd never have thought it might be a Czech word originally!

Anyway, I think Magdalena is right about the "iż". I have simply confounded it with the word "ponieważ", and it is of this word that my printed source of the history of the Polish language states that it was a borrowing from Czech and is seldom used in speech, belonging basically to the world of writing.

yes! I agree , but "że" is not a good word ...
noone says "iż" nowodays we use, ponieważ, lub, bo means "because" or depends on sentence...

Obywaciel for me sounds like cielak - obywacielak anybody?

Somehow I don't have such connotations with nauczyciel and przyjaciel.

I speak ;) maybe not so often but it happens. In written language is quite common.