Coming back to differences between sunnis and shias, here are some major ones:
Difference of opinion in authenticiy of Quran:
Sunnis view: There is unanimous agreement among them regarding its authenticity, and its text being safeguarded from any additions or deletions. The Qur'an is to be understood in consonance with the rules and bases of the Arabic language. They believe in every single letter of it, it being the word of Allah the Exalted. The Qur'an is neither temporal nor newly created, but is eternal. Falsehood does not approach it from before it or behind it. It is the primary source of all the Muslims' tenets of faith, their rites and rules of conduct.
Shias view:To some of them, the Qur'an's authenticity is doubtful, and if it appears to contradict any of their sectarian beliefs or doctrines, then they give the Qur'anic text strange, far-fetched interpretations that agree with their sectarian views. For that reason they are called Al-Mutawwilah (those who give their own interpretations to the revealed texts). They love to draw attention to the discord that occurred at the time when the Qur'an was first compiled. The views and opinions of their Imams are the primary source of their jurisprudence.
Hadeeths (The Prophetic Traditions)
For the Sunnis, it is the second source of revealed law, complementary to the Noble Quran It is not permissible to contradict or reject the rulings and directives contained in those Hadeeths (ahaadeeth) which are reliably attributed to the Prophet (may Allah's blessings and peace be upon him). The methodology applied in determining the authenticity of these traditions utilizes a set of stringent rules agreed upon by the scholars who specialize in this field, and involves detailed analysis of the chain of transmitters of any given tradition. No distinction is made between male and female narrators; judgment is made solely on the basis of individual trustworthiness and technical ability in relating traditions, and every narrator's history is recorded. No tradition is accepted from a known liar, or from one whose morals or scholarly ability were not corroborated, or from anyone, merely on the basis of his family connection or lineage. The compilation of the Prophetic Traditions is taken to be a sacred Trust, the fulfillment of which overrides all other considerations.
The Shi'ites reject all Prophetic Traditions which were not related by members of Ahlul-Bait, or their descendants. The only exception to this rule is their acceptance of a few Hadeeths (ahaadeeth) narrated by those who sided with 'Ali (may Allah be pleased with him) in his political wars. They do not attend to the authenticity and soundness of the chain of narrators, nor do they approach the study of the Prophetic Traditions with a scientific, critical attitude. Their narrations often appear in a form like that of the following example: "It has been reported regarding Muhammad bin Isma'eel by way of some of our friends through a man who transmitted it from him 'Ali] that he said..." Their books are filled with hundreds of thousands of traditions whose authenticity cannot be confirmed. They have built their religion specifically upon these spurious texts while outright rejecting over three quarters of the authentic Prophetic Traditions. This is one of the main differences between the Shi'ites and the Sunnis.
The Companions Of The Prophet
It is unanimously agreed that the noble Companions deserve our utmost respect, and are absolutely trustworthy. As for the discord which occurred among them, it is to be considered as the consequence of the sincere exercise of personal conviction and opinion. The discord was resolved and is a thing of the past. It is not permissible for us to hold, on the basis of past differences among the Companions, grudges and ill will which continue for generations. The Companions are those whom Allah has described in the best of terms; He has praised them upon many occasions. It is not lawful for anyone to make any accusation against them or cast suspicion upon them, and there is no benefit to be derived therefrom.
They charge that all save a few of the Companions had turned apostate after the death of the Prophet (may the peace and blessings of Allah be upon him). On the other hand, they grant the Companion 'Ali bin Abi Taalib a very special status; some of them consider him vicegerent, and some view him as a prophet, while others take him for a god! Shi'ites pass judgment on Muslims in accordance with their position with regards to 'Ali. Whoever was elected caliph before 'Ali is held by them to be a tyrant, an apostate or a sinner. The same judgment is passed on every Muslim ruler who did not step down for any of the descendants of 'Ali and his wife Fatimah (may Allah be pleased with them). The Shi'ites have thus created an atmosphere of animosity throughout the history of Islam, and the question of partisanship of Ahlul-Bait developed into a school of thought which preached and perpetuated such detrimental teachings down through the generations.
Belief In The Oneness Of Allah
Sunnis believe that Allah is the One, the Only, God, the Almighty Subduer. He has no partners or rivals, and He has no equal. There is no intermediary between Him and His worshippers. They believe in His attributes as they were revealed In the Qur'anic verses, and they do not obscure their obvious meanins with far-fetched Interpretations. They do not strike any comparison between the divine attributes and other things, for as Allah says in His Book "There is nothing like unto Him." They believe that Allah sent the Prophets and commissioned them with conveying to mankind His Message and Guidance. They conveyed Allah's Message and did not conceal any part of it They believe that knowledge Of the unseen belongs to Allah alone. Intercession is confined to the Hereafter, and none may intercede except by Allah's permission. All supplication, vows, offerings of sacrifices and requests for needs are to be directed to God alone; they are not to be directed to any other besides Him. Allah alone controls good and evil. There is no one, living or dead in His authority or in His administration of affairs. All beings depend on Him, and need His favor and mercy. The knowledge of Allah is attained through knowledge of divinely revealed law, and this has precedence over the exercise of reason, which might never guide one to the truth, although it may provide reassurance to the believer, and help him to achieve tranquillity.
The Shi'ites also believe in Allah the Exalted and His Oneness, except that they adulterate this belief with polytheistic rituals and observances. They implore and make supplication to Allah's slaves and worshippers rather than to Him alone, saying "O Ali! and "O Husain!" and "O Zainab!" Similarly they make vows and sacrifice beasts in the name of others besides Allah. They request the dead to fulfil their needs as is shown by their prayers and poems. They consider their Imams to be infallible, to have knowledge of the unseen, and to partake In the administration of the universe. It is the Shi'ites who Invented Sufism (mysticism) to consecrate their deviated tenets and thus give them the air of legitimacy They claimed that there is special power and authority invested in the "awliyaa"' (mystic saints), "aqtaab" (those considered to be the spiritual axes of the universe, which turns due to their exalted status), and Ahlul-Bait Shi'ite scholars and clergy impressed upon their followers the concept of a hereditary privileged class, as a matter of religion, although this has no foundation in Islam at all. Knowledge of Allah, is attained, according to them, through the exercise of reason, not by knowledge of divinely revealed law. That which came to us by way of revelation in the Qur'an merely represents an affirmation of reason's judgment; it is not considered to be a source which is independent of, and beyond the limits of reason.
Governing The Islamic State
The state is ruled by a Caliph (Khalifa) elected to his position of leadership from among the Muslim people. To be leader, a man must be sane, rightly guided and knowledgeable. He should be known for his piety and trustworthiness, and he should be capable of bearing such a responsibility. The caliph is nominated to his position Of leadership by those Muslims endowed with knowledge and experience. If he does not hold firm to his duty, and deviates from the directives of the Qur'an, then they may remove him from his position and strip him of all authority. Otherwise, he deserves the obedience and cooperation of every Muslim. The role of caliphate is, to the Sunnis, a great burden and responsibility, not a mere honor or opportunity for exploitations.
Generally speaking, the right to govern according to Shi'ites, is hereditary, and restricted to 'Ali, and his descendants by Fatimah (the daughter of the Prophet). There is, however, some slight difference among them on the point of the hereditary right as to whom it belongs to. Due to this view of theirs, the Shi'ites are never loyal to any ruler unless he is one of the descendants of 'Ali bin Abi Taalib. When the practice of hereditary leadership vested in the descendants of 'Ali and Fatimah could no longer be maintained, because the line had come to an end, the Shi'ites invented the doctrine of Ar-Raj'ah, according to which the last Imam was not dead, but "hidden". He is expected to arise and return at the end of time, when he will slaughter all of his political opponents, and those of his ancestors, and will restore to the Shi'ites their rights which were "plundered" by the other sects over the centuries.
** Again how can you combine them under one hand of 'khilafat' considering such differences**
I will post more differences between these two sects later on...