One of the women with whom marriage has been prohibited for every man in the Quran is stepdaughter. This prohibition is stated in the Quran with the phrase “Prohibited to you are … your stepdaughters who are in your care being born of your wives you have been in to” on the condition that the man, in addition to marriage contract, has done intercourse with the mother of the stepdaughter. There may be different instances of intercourse like reluctant intercourse, intercourse in sleeping or unconsciousness, intercourse from behind, and so forth. The present research aims to show whether intercourse from behind or other types of unusual intercourse can be considered the instances of “you have been in to” in order to rely on generalization? For this reason, studying the Arabic literature and lexicographers' information, the meaning of “being in to” has been analyzed first. Next, the findings of the research have been taken as criteria for evaluating the Islamic jurists' relying on the same verse. Finally, it has been found that the phrase “you have been in to” in the Quran applies only to the consummation of the marriage but not all kinds of sexual contact. Therefore, it can not be generalized to all kinds of sexual contact. Withdrawing the generalization also leads to the conclusion that “prohibition of marriage with some stepdaughters”, although reputed in Imamite Islamic jurisprudence following Allameh Helli, is not provable based on generalization; although, there are other jurisprudential methods other than relying on generalization to prove this judicial decree which can be studied