1. MEANING OF IMAMATE AND KHILAFAH
AL-IMAMAH literally means 'to lead '; al-imam means 'the leader'. In Islamic terminology al-imamah (Imamate) means 'universal authority in all religious and secular affairs, in succession to the Prophet' . al-Imam means 'the man who, in succession to the Prophet, has the right to the absolute command of the Muslims in all religious and secular affairs '.
The word 'man' signifies that a female cannot be an Imam. 'Absolute command' excludes those who lead in the prayers: they are also called 'Imam of the prayers', but they do not have absolute authority. 'In succession to the Prophet ' denotes the difference between a prophet and an Imam. The Imam enjoys this authority not directly, but as the successor of the Prophet.
The word al-khilafah means 'to succeed' and al-khalifah means 'the successor'. In Islamic terminology al-khilafah and al-khalifah practically signify the same meanings as al-ima'mah and al-ima'm repectively.
al-Wisayah means ' the executorship of the will', and al-wasiyy means 'the executor of the will'. Their significance in Muslims' writings is the same as that of al-khilafah (caliphate) and al-khalifah (caliph).
It is interesting to note that many previous prophets were also the caliphs of their predecessor prophets, thus they were nabiyy and khalifah both; while other prophets (who brought new shari'ah) were not caliphs of any previous prophets. Also there were those who were caliphs of the prophets but not prophets themselves.
The question of Imamate and caliphate has torn the Muslim community apart and has affected the thinking and philosophy of the different groups so tremendously that even the belief in Allah (at-tawhid) and the prophets (an-nubuwwah) could not escape from this divergence of views.
This is the most debated subject of Islamic theology. Muslims have written thousands upon thousands of books on caliphate. The problem before me is not what to write; it is what not to write. In a small work such as this, one cannot touch on all the various aspects of this subject, let alone go into detail on even those topics which are described therein. This provides only a brief outline of the differences regarding the caliphate.
It may be of help to mention here that regarding this question the Muslims are divided into two sects: the Sunnis, who believe that Abu Bakr was the first caliph of the Holy Prophet of Islam; and the Shi'ahs, who believe that 'Ali Ibn Abi Talib, peace be upon him, was the first Imam and caliph.
This fundamental difference has led to other differences which shall be described in the following chapters.
2. SUMMARY OF DIFFERENCES
The Holy Prophet has said in a hadith which has been accepted by all sects of Islam:
My ummah ( followers) will shortly break up into seventy-three sects, all of which shall be condemned except one. 
The seekers of salvation have always made untiring efforts to inquire into the matter to discover the right course - the path to salvation. And indeed it is necessary for every man to take reason as his guide, try his best in this matter and never despair of attaining the truth. But this can only be possible when he has a clear view of the radical differences before him, and discarding all bias and prejudices, examines the points at issue with thoughtful mind, always praying to Allah to lead him in the right path.
For this reason I propose to briefly mention here the important differences and conflicts together with the arguments and reasonings of each sect, in order to facilitate the path of inquiry. The main questions are:
1. Does it lie with Allah to appoint a prophet's successor or is it the duty of the ummah (the followers) to appoint whomsoever they please as successor to the Prophet?
2. In the latter case, did Allah or the Prophet place in the hands of the ummah any systematic code containing the rules and procedures for the appointment of a caliph, or did the ummah by their unanimous consent before appointing a caliph, prepare a set of rules to which they adhered (subsequently), or did the ummah act according to what they thought expedient at the time and according to the opportunity at their disposal? Had they the right to act as they did?
3. Does reason and Divine Law demand the existence of any qualifications and conditions in an Imam and caliph? If so, what are they?
4. Did the Prophet of Islam appoint anyone as his caliph and successor or not? If he did so, who was it? If not, why?
5. After the Prophet's death, who was recognized to be his caliph and did he possess the qualifications necessary for a caliph? 
3. BASIC DIEFERENCE
It will save time if we explain at the outset the basic cause of the differences concerning the nature and character of the Imamate and caliphate. What is the primary charactenstic of the Imamate? Is an Imam, first and foremost, the ruler of a kingdom? Or is he, first and foremost, the representative of Allah and vicegerent of the Prophet?
As the Imamate and caliphate is generally accepted as the successorship of the Prophet, the above questions cannot be answered until a decision is made on the basic characteristics of a prophet. We must decide whether a prophet is, first and foremost, the ruler of a kingdom or the representative of Allah.
We find in the history of Islam a group which viewed the mission of the Holy Prophet as an attempt to establish a kingdom. Their outlook was material; their ideals were wealth, beauty and power. They, naturally, ascribed the same motives to the Holy Prophet. 'Utbah ibn Rabi'ah, the father-in-law of Abu Sufyan, was sent to the Holy Prophet to convey the message of the Quraysh: "Muhammad! If you desire power and prestige, we will make you the overlord of Mecca. Do you desire marriage into a noble family? You may have the hand of the fairest maiden in the land. Do you desire hoards of silver and gold? We can provide you with all these and even more. But you must forsake these nefarious preachings which imply that our forefathers who worshipped these dieties of ours were fools."
The Quraysh were almost certain that Muhammad (saw) would respond favourably to this offer. But the Holy Prophet recited surah 41 in reply which, inter alia, contained the following warning:
But if they turn away, then say: "I have warned you of a thunderbolt (of punishment) like the thunderbolt of the 'Ad and the Thamud " (41: 13)
'Utbah was overwhelmed by this clear warning. He did not accept Islam, but advised the Quraysh to leave Muhammad (saw) alone to see how he could fare with other tribes. The Quraysh claimed that he was also bewitched by Muhammad (s. a.w. a.)  .
Thus he wanted to leave Muhammad (s.a.w. a.) to other tribes. On the other hand when the Prophet emigrated to Medina and the Quraysh waged war upon war, the other tribes thought it advisable to leave Muhammad (saw) to his own tribe. 'Amr ibn Salamah, a companion of the Prophet, states: "The Arabs were waiting for the Quraysh to accept Islam. They used to say that Muhammad (saw) should be left to his own people. If he would emerge victorious over them, he was undoubtedly a true prophet. When Mecca was conquered, all the tribes hastened to accept Islam." 
Thus according to them, victory was the criterion of truth! If Muhammad (saw) would have been defeated, he would have been considered a liar ! !
The view that his sacred mission was nothing but a worldly affair was repeatedly announced by Abu Sufyan and his clan. At the time of the fall of Mecca, Abu Sufyan left Mecca to discern the strength of the Muslim army. He was seen by the uncle of the Prophet, 'Abbas, who took him to the Holy Prophet and advised the Prophet that he be given protection and shown respect, in order that he may accept Islam.
To summarize the event, 'Abbas took Abu Sufyan for a review of the Islamic army. He pointed out to Abu Sufyan eminent personalities from every clan who were present in the army. In the meantime, the Holy Prophet passed with his group which was in green uniform. Abu Sufyan cried out: "O 'Abbas ! Verily your nephew has acquired quite a kingdom ! " 'Abbas said: "Woe unto thee! This is not kingship; this is Prophethood". 
Here we see two opposing views in clear contrast. Abu Sufyan never changed his views. When 'Uthman became caliph, Abu Sufyan came to him and advised: "O Children of Umayyah! Now that this kingdom has come to you, play with it as the children play with a ball, and pass it from one to another in your clan. This kingdom is a reality; we do not know whether there is a paradise or hell or not." 
Then he went to Uhud and kicked at the grave of Hamzah (the uncle of the Prophet) and said: "O Abu Ya'la! See that the kingdom which you fought against has at last come to us." 
The same views were inherited by his grandson, Yazid, who said:
Banu Hashim staged a play to obtain the kingdom;
If that is the view held by any Muslim, then he is bound to equate the Imamate with rulership. According to such thinking, the primary function of the Prophet was kingship, and, therefore, anyone holding the reins of power was the rightful successor of the Holy Prophet.
But the problem arises in-that more than ninety per cent of the prophets did not have political power; and most of them were persecuted and apparently helpless victims of the political powers of their times. Their glory was not of crown and throne; it was of martyrdom and suffering. If the primary characteristic of prophethood is political power and rulership, then perhaps not even 50 (out of 124,000) prophets would retain their divine title of nabiyy.
Thus it is crystal-clear that the main characteristic of the Holy Prophet was not that he had any political power, but that he was the Representative of Allah. And that representation was not bestowed on him by his people; it was given to him by Allah Himself.
Likewise, his successor's chief characteristic cannot be political power; but the fact that he was the Representative of Allah. And that representation can never be bestowed upon anyone by his people; it must come from Allah Himself. In short, if an Imam is to represent Allah, he must be appointed by Allah.
4. SYSTEM OF ISLAMIC LEADERSHIP
There was a time when monarchy was the only system of government known to the people. At that time the Muslim scholars used to glorify monarchs and monarchy by saying, The king is the shadow of Allah, as though Allah has a shadow! Now in modern times democracy is in vogue and the Sunni scholars are never tired of asserting in hundreds and thousands of articles, books and treatises that the Islamic system of government is based upon democracy. They even go so far as to claim that democracy was established by Islam, forgetting the city-republics of Greece. In the second half of this century, socialism and communism are gaining hold of the undeveloped and developing countries; and I am not surprised to hear from many well-meaning Muslim scholars tirelessly asserting that Islam teaches and creates socialism. Some people in Pakistan and elsewhere have invented the slogan of 'Islamic socialism'. What this 'Islamic socialism' means, I do not know. But I would not be surprised if within ten or twenty years these very people start claiming that Islam teaches communism!
All this 'changing with the wind' is making a mockery of the Islamic system of leadership. Some time ago in a gathering of Muslims in an African country, in which the president of the country was the guest of honour, a Muslim leader stated that Islam taught to 'Obey Allah, obey the Apostle and your rulers'. In his reply, the president (who incidently, was a staunch Roman Catholic) said that he appreciated very much the wisdom of the commandment to obey Allah and the Apostle of Allah; but he could not understand the logic behind the order to obey 'your rulers'. What if a ruler is unjust and a tyrant'! Does Islam enjoin Muslims to obey him passively without resistance?
This intelligent question demands an intelligent reply. It cannot be regarded lightly. The fact is that the person who invited that criticism, did so because of his misinterpretation of the Holy Qur'an.
Let us examine the system of Islamic leadership. Is it democratic? The best definition of democracy was given by Abraham Lincoln when he said that democracy was "the government of the people, by the people and for the people".
But in Islam it is not the government 'of the people'; it is the 'government of Allah'. How do people govern themselves? They govern themselves by making their own laws; in Islam laws are made not by the people, but by Allah; these laws are promulgated not by the consent and decree of the people, but by the Prophet, by the command of Allah. The people have no say in legislation; they are required to follow, not to make any comment or suggestion about those laws and legislations:
And it is not for a believer man or believer woman to have any choice in their affair when Allah and His Apostle have decided a matter. . . (33:36).
Coming to the phrase 'by the people', let us now consider how people govern themselves. They do so by electing their own rulers. The Holy Prophet, who was the supreme executive, judicial and overall authority of the Islamic government, was not elected by the people. In fact, had the people of Mecca been allowed to exercise their choice they would have elected either 'Urwah ibn Mas'ud (of at-Ta'if) or al Walid ibn al-Mughirah (of Mecca) as the prophet of Allah! According to the Qur'an:
And they say:"Why was not this Qur'an revealed to a man of importance in the two towns?" ( 43 :31 ) 
So not only was the Supreme Head of the Islamic State appointed without the consultation of the people, but in fact it was done against their expressed wishes. The Holy Prophet is the highest authority of Islam: he combines in his person all the functions of legislative, executive and judicial branches of the government; and he was not elected by the people.
So Islam is neither the government of the people nor by the people. There is no legislation by the people; and the executive and judiciary is not responsible to the people.
Nor is it, for that matter, a government 'for the people'. The Islamic system, from the beginning to the end, is 'for Allah'. Everything must be done 'for Allah'; if it is done 'for the people', it is termed 'hidden polytheism'. Whatever you do-whether it is prayer or charity, social senice or family function, obedience to parents or love of neighbour, leading in prayer or deciding a case, entering into war or concluding a peace-must be done with "qurbatan ila'llah", to become nearer to Allah, to gain the pleasure of Allah. In Islam; everything is for Allah.
In short, the Islamic form of government is the government of Allah, by the representative of Allah, to gain the pleasure of Allah.
And I did not create the jinn and the human beings except that they should worship me (51:56).
It is theocracy, and it is the nature and characteristic of Islamic leadership. And how it affects the meaning of the above verse concerning 'obedience' shall be seen in later chapters.
al-'Allamah al-Hilli: al-Babu 'l-hadi 'ashar, Eng. tr. W. M. Miller,
p. 62; Mughniyyah: Falsafat Islamiyyah, p. 392.
al-Khatib at-Tabrizi: Mishkatu 'l-masabih, Eng. tr. James Robson,
vol.l, p.45; al-Majlisi has collected, in a complete chapter, traditions
to this effect in Biharu 'l-anwar,, vol. 28, pp. 2-36; al-Qummi,
Sh. 'Abbas: Safinatu 'l-bihar, vol. 2, pp. 359-60 .
an-Nubuwwah wa 'l-khilafah, tr. Liqa' 'Ali Haydari,
pp. 2 3.
as-Sirah an-Nabawiyyah, vol.l, pp. 313 -4.
as-Sahih, vol. 5, p. 191; Ibn Kathir: al-Bidayah
wa 'n-nihayah, vol. 5,p. 40.
al-Mukhtasar, vol.1, pp 143-4; alYa'qubi: at-Tarikh,
vol. 2, p. 59.
Ibn 'Abdi 'l-Barr: al-lsti'ab, vol. 4, p.l679; Ibn Abi 'l-Hadid
quotes the last sentence as follows: "By him in whose name Abu Sufyan swears,
there is neither punishment nor reckoning, neither Garden nor Fire, neither
Resurrection nor Day of Judgment." (Vide his Sharh Nahji 'l-balaghah,
vol. 9, p. 53.)
Ibn Abi 'l-Hadid: op. cit., vol. 16, p. 136.
Sibt ibn al Jawzi: 'Tadhkirah, ed. S. M. S. Bahru 'l 'Ulum, p. 261;
at-Tarikh, vol.13, p. 2174.
 For the explanation of "a man of importance", see, as-Suyuti: Lubabu u'n-nuqul fi asbabi'n-nuzul printed with Tafsiru 'l-jalalayn, pp. 289, 649.