Re: Reasons for polygamy
***If a husband takes a second wife, he has to treat his wives equally as far as possible. If he does not treat them equally then he is exposing himself to a stern warning, for it was narrated from Abu Hurayrah that the Prophet (peace and blessings of Allaah be upon him) said: “Whoever has two wives and inclines more towards one of them than the other, will come on the Day of Resurrection with half of his body leaning.” (narrated by al-Nisaa’i, ‘Ushrat al-Nisaa’, 3881; classed as saheeh by al-Albaani in Saheeh Sunan al-Nasaa’i, no. 3682).
When Allaah permitted us to marry more than one woman, He said (interpretation of the meaning):
“but if you fear that you shall not be able to deal justly (with them), then only one or (slaves) that your right hands possess. That is nearer to prevent you from doing injustice”[al-Nisaa’ 4:3]
So Allaah commands that a man should restrict himself to one wife, if he knows that he cannot be just. And Allaah is the source of strength.
See Fataawa Manaar al-Islam, 2/570.
Sheikh Muhammed Salih Al-Munajjid
***After reading up, I am inclined to agree with you Princessjojo, a man does not require the “permission” of his wife to marry again.
He is enjoined to tell her though.