What is the difference between Islam and Iman?

What is Islam and how does it stand in relation to Iman appears to have become an issue in the first half of the second century as it gained a place in Abu Hanifah's book "al-Fiqh al-Akbar" where it state from a linguistic perspective there is a difference between iman and Islam. Iman means "al-iqrar wa al-tasdiq" and Islam means "al-inqiyad wa al-tasli". However one is not possible without the other, iman is not possible without Islam nor Islam without iman. The commentator adds Abu Hanifah advocates the view of scholars who hold the two words are synonymous. Al-Ash'ari in his aI-Ibana declares Islam is more general than iman and not every Islam is iman, meaning the application of the term Islam is wider and could be applied to anyone who called himself a Muslim, whereas mumin is limited in its application. Strange as it may seem, this view reflects the Mutazilites'  stand which is well summed up by al-Bazdawi: "According to the Mutazilites and Rafidites, one is different from the other. Therefore, in their view, a person who commits a grave sin is a muslim but not a mu'min. So, if someone made a will in favour of poor mumin the money will not be distributed to those guilty of grave sins, nor indeed to the Sunnites. The money in such a case will only be given to the Mutazilites and the Shi'ites. But if the will is in favour of poor muslimun, the money could be given to the poor from all the people of Qiblah." In all the cases where difference between iman and Islam was advocated, the verse 44:14 was quoted in support. The above discussion shows the causes underlying the controversy as well as the direction it was taking. The whole situation is summed up by al-Shahristani in his "al-Milal wa -Nihal". After quoting the famous tradition, in which islam, iman and ihsan are defined, he goes on to say: "So the Prophet has differentiated in the meaning of the words al-Islam and al-iman. Al-Islam therefore, may be used to mean outward submission and as such it is equally applicable to a believer and a hypocrite." After quoting the verse 44:14 he says, "It shows that even the Qur'an differentiated between the two." Al-Shahristani then adds : "On this basis the world al-muslimun will cover both those who will be saved and those who will perish." Here al-Shahristani is not giving a sectarian view, rather it is presented as a universally accepted opinion on the basis of which he proposed to include in his book all kinds of sects in its chapter on al-muslimun. Muslim had thus become the accepted nomenclature, completely replacing mu'min of the earlier usage. This replacement is noticeable in earlier theological works where, even while discussing iman, the nomenclature adopted is muslim. Hadith reflects this process of change in its more frequent usage of the words aslama, islam and muslimun than iman, amana and mu'minun in contrast to the Quran. Today a person reads formulae of iman, becomes a muslim. The adoption of the name al-Ikhwan  al-Muslimuns while based on the Quranic concept of 44:10 is a clear example of this complete replacement, that has taken place.