But young Iranians do not seem to be listening.
"It's too expensive to get married and even more expensive to get a divorce," says Ali from Tehran, who has been living with his girlfriend for two years.
Zanan magazine devoted a recent issue to the subject of cohabitation
"Why commit myself to something I'm not sure about?"
It is attitudes like this that show just how far some young urban Iranians have moved away from the Islamic values of their parents' generation.
"Of course cohabitation is not accepted by the more religious parts of society," says sociologist Mehrdad Darvishpour, who is now based in Sweden.
"But just like in the rest of the world, the middle class in Iran is starting to prefer this type of life to traditional marriage. Sex before marriage isn't taboo anymore."
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