The sexual instinct is one of the most powerful instincts that resides in human beings, and much like other basic needs, it must be fulfilled in the correct method and manner. These basic instincts cannot be suppressed or eliminated and even if it were possible to suppress them, it would not be logical to do so and it goes against the very makeup of the human body. So the correct way is to satisfy these instincts in a legitimate and reasonable manner.
At the same time, there are many people who are not in a situation where they can be married permanently. Some of these people are faced with long journeys, or official posts in remote places, or other situations where they face the issue of their unmet sexual needs. For answering situations like these, Islam has given the option of multiple permanent marriages or temporary marriages in addition to a monogamous marriage and it has put these in a regulated framework with rules and regulations.
We must also keep in mind that:
1. We Muslims believe in a God who is benevolent and caring towards his servants and he never enacts rules and regulations for them without a purpose. In essence it can be said that the rules that are made by God are created for the benefit of people and for preventing harm to them.
2. If temporary marriage and polygamy were blocked, then society and the individual would be irreparably harmed. So Islam, which has a set of divinely guided rules and regulations, has made polygamy and temporary marriage permissible and this permission has been given to men without making it conditional on the first wife’s consent. The reason for this is that if the right was made conditional on the wife’s permission and consent, then the majority of women due to their female nature and emotions would not allow this to go forward and the main purpose of why God allowed this form of marriage would never be allowed to manifest itself.
In addition to these main rules some Jurisprudents have said that: If a Muslim man wishes to temporarily marry a woman from the ‘Ahlul Kitab’, and he has a permanent Muslim wife, then the permission of that Muslim wife is a condition for the new marriage.
The sexual instinct is one of the many instincts which God has gifted to man. Answering this instinct is one of the natural and essential needs of human beings; this being contrary to certain monastic style religions which recommend a life of celibacy. Suppressing this natural instinct is not a recommended formula for life and will be the cause of many emotional disturbances. At the same time social chaos, lack of social laws and boundaries, sexual communism, and excessively going after these desires is against the very purpose of human creation. From this perspective the best and most natural form for relationships between men and women has these particularities:
1. Matrimonial union based on laws
2. Having a single spouse
3. Permanent marriage
If a permanent marriage is not possible due to various reasons and there was no possibility of becoming permanently married then society or the individual would become afflicted with various problems and disorders. In situations such as these should we simply announce a type of sexual communism and encourage relationships with no boundaries or laws? Or should we create a new form of marriage (permanent and temporary) which prevents as much as possible, wanton sensuality and the taking advantage of men and women. In a situation like this two possibilities and viewpoints exist:
1. The viewpoint of pure Islam which was expounded upon by the Holy Prophet (s) and the Infallibles (a) which allowed polygamy and also temporary marriage. (Keep in mind that for forming a family the emphasis is on monogamy and permanent marriage. But for emergency cases where there are no options these options of polygamy and temporary marriage have also been made available.
2. The other viewpoint is that a man has relationships with more than one permanent wife in an unlawful way. Certain individuals and groups in the west are proponents of a sort of sexual communism and freedom from responsibilities and obligations of marriage. There are many scholars and sincere thinkers who have proposed their heartfelt conviction that there is a great social necessity for a type of temporary marriage and if this form of marriage is prevented then society and the individual will be harmed irreparably.
In human society, especially modern society, sexual relations cannot be constrained only to permanent marriage and no society or government has been able to stop these relationships (non permanent marriage) from taking place. Unfortunately most societies have allowed unlawful forms of sexual relationships to take place in order to meet these needs and fornication and centers of prostitution have been legally opened and sanctioned. This form of profit making from young girls and older women is not sanctioned by Islam and is an insult and an abuse of women. Even more importantly it is a leading social cause for the disintegration of the family unit. So the only real solution that is left and can be considered lawful before God is that of temporary marriage or polygamy. This means that men and women, through a specified religiously prescribed format, will join together in wedlock, in a way that will ensure everyone’s rights and make sure that human morals and religious laws are not broken. It must be kept in mind that the difference between permanent and temporary marriage is in the specified time period; In view of all the problems modern societies face today temporary marriage is the best way for solving various problems which permanent marriage cannot solve or through which various problems will come about.
By paying attention to this point we realize that God is merciful towards his servants and cares about them; He never enacts laws without having definite purposes behind them. Islam, which is the instrument through which divine law is brought down, due to necessity and reason, has given the right of temporary marriage and polygamy to the husband. God, for the use of this right, has not made it conditional on the wife’s permission. In fact if this right was made conditional upon the wife’s approval, keeping in mind women’s emotional nature and their sensitivity towards this matter, which is against their husbands having any other wives, then the reason behind why this law was created would never be allowed to manifest itself and it would defeat the whole purpose. With this in mind, some jurisprudential scholars are of the opinion that if a Muslim man wishes to temporarily marry a ‘Ahlul Kitab’ (People of the Book) wife, while he has a permanent Muslim wife, then the permission of that first Muslim wife is a condition upon the second marriage.
 For further information, see: The permissibility of polygamy for men, Question 693.
 It is in view of this that jurisprudents have said that women cannot deny their husbands this right. Imam Khomeini, Istifta’at, vol. 3, pg. 100, Question 55.
 See: Siratul-Nijat, Sheikh Jawad Tabrizi, vol. 2, pg. 270. Related Question: Temporary marriage with women of the People of the Book, Question 1209.