This long article is a part of Martyr Murtada Mutahhari's book Ashna'i ba 'ulum-e Islami (An Introduction to the Islamic Sciences). The book consists of seven parts: (1) logic (2) philosophy (3) al-kalam (Muslim scholastic philosophy) (4) 'irfan (Islamic mysticism) (5) usul-e fiqh (the principles of jurisprudence) (6) fiqh (Islamic jurisprudence) (7) hikmat-e 'amali' (practical philosophy or practical morality).
All the seven parts together serve both as a comprehensive survey of the fundamentals of different branches of Islamic sciences and a general and comprehensive perspective for the proper understanding of the basic teachings of Islam along with the main points of difference among various sects of Muslims.
This work of Martyr Mutahhari is the best introduction to Islamic philosophy and jurisprudence. From this view, Ashna'i ba 'ulum-e Islami deserves to be prescribed as the basic text for all the students of Islamic studies. It is also very useful for non-specialists who wish to acquaint themselves with Islam.
All the introductory books written so far are either by the Orientalists and are naturally biased and fail to give true picture of the development of different Islamic sciences or are written by Muslim scholars who consciously or unknowingly incorporate in the body of books certain misleading notions propagated by the Western scholars of Islam about Muslirn philosophy and its various branches. It also can be said with some justification that no other available introductory text in this field covers all Muslim sects and their specific views. Martyr Murtada Mutahhari's exposition and evaluation
of various theories is objective and unbiased, which is the most essential condition for a book to be prescribed as an introductory text.
In this part, dealing with 'ilm al-kalam, the author has discussed the main doctrines of kalam and their subsequent modifications with special reference to Mu'tazilah, Asha'irah and Shi'ah schools of kalam. But he has not ignored other schools and has referred to their relevant doctrines wherever it was necessary for the full understanding of the problem under discussion.]
'Ilm al-kalam is one of the Islamic sciences. It discusses the fundamental Islamic beliefs and doctrines which are necessary for a Muslim to believe in. It explains them, argues about them, and defends them.
The scholars of Islam divide Islamic teachings into three parts:
(i) Doctrines ('aqa'id): These constitute the issues which must be understood and believed in, such as, the Unity of God, the Divine Attributes, universal and restricted prophethood, etc. However, there are certain differences between Muslim sects as to what constitutes the basic articles of faith (usul al-Din) in which belief is necessary.
(ii) Morals (akhlaq): These relate to the commands and teachings relating to the spiritual and moral characteristics of human beings, such as, justice, God-fearing (taqwa), courage, chastity, wisdom, endurance, loyalty, truthfulness, trustworthiness, etc., and prescribe 'how' a human being should be.
(iii) The Law (ahkam): Here the issues relating to practice and the correct manner of performing acts, such as, prayers (salat), fasting (sawm), hajj, jihad, al- 'amr bil ma'ruf wa al-nahy 'an al-munkar, buying, renting, marriage, divorce, division of inheritance and so on, are discussed.
The science which deals with the first of the above-mentioned is 'ilm al-kalam. The study of the second is 'ilm al-'akhlaq (ethics). The study of the third is called 'ilm al-fiqh (the science of jurisprudence). That which is subjected to division in this classification is the corpus of Islamic teachings; that is, those things which constitute the content of Islam. It does not include all those Islamic studies which form the preliminaries for the study of Islamic teachings, such as, literature, logic, and occasionally philosophy.
Secondly, in this classification the criterion behind division is the relationship of Islamic teachings to the human being: those things which relate to human reason and intellect are called 'aqa'id; things which relate to human qualities are called akhlaq; and those things which relate to human action and practice are included in fiqh.
As I shall discuss in my lectures on 'ilm al-fiqh, although fiqh is a single discipline from the viewpoint of its subject, it consists of numerous disciplines from other viewpoints.
In any case, 'ilm al-kalam is the study of Islamic doctrines and beliefs. in the past, it was also called "usul al-Din" or "'Ilm al-tawhid wa al-sifat".

The Beginnings of Kalam:
Though nothing definite can be said about the beginnings of 'ilm al-kalam among Muslims, what is certain is that discussion of some of the problems of kalam, such as the issue of predestination (jabr) and free will (ikhtiyar), and that of Divine Justice, became current among Muslims during the first half of the second century of Hijrah. Perhaps the first formal centre of such discussions was the circle of al-Hasan al-Basri (d. 110/728-29). Among the Muslim personalities of the latter half of the first century, the names of Ma'bad al-Juhani (d. 80/ 699) and Ghaylan ibn Muslim al-Dimashqi (d. 105/723) have been mentioned, who adamantly defended the ideas of free will (ikhtiyar) and man's freedom. There were others who opposed them and supported predestination (jabr). The believers in free will were called "qadariyyah" and their opponents were known as "jabriyyah".
Gradually the points of difference between the two groups extended to a series of other issues in theology, physics, sociology and other problems relating to man and the Resurrection, of which the problem of jabr and ikhtiyar was only one. During this period, the "qadariyyah" came to be called "Mu'tazilah" and the "jabriyyah" became known as "Asha'irah ". The Orientalists and their followers insist on considering the beginnings of discursive discussions in the Islamic world from this point or its like.
However, the truth is that rational argumentation about Islamic doctrines starts with the Holy Qur'an itself, and has been followed up in the utterances of the Holy Prophet (S) and especially in the sermons of Amir al-Mu'minin 'Ali (A). This despite the fact that their style and approach are different from those of the Muslim mutakallimun. [1]

The Holy Qur'an has laid the foundation of faith and belief on thought and reasoning. Throughout, the Qur'an insists that men should attain faith through the agency of thought. In the view of the Qur'an, intellectual servitude is not sufficient for believing and understanding its basic doctrines. Accordingly, one should take up a rational inquiry of the basic principles and doctrines of the faith. For example, the belief that God is One, should be arrived at rationally. The same is true of the prophethood of Muhammad (S). This requirement resulted in the establishment of 'ilm al-'usul during the first century.
There were many reasons which led to the unprecedented realization of the necessity for the study of the fundamentals of the Islamic faith amongst Muslims and the task of defending them, a realization which led to the emergence of prominent mutakallimun during the second, third, and fourth centuries. These were: embracing of Islam by various nations who brought with them a series of (alien) ideas and notions; mixing and coexistence of the Muslims with people of various religions, such as, the Jews, the Christians, the Magians, and the Sabaeans, and the ensuing religious debates and disputes between the Muslims and those peoples; the emergence of the Zanadiqah [2] in the Islamic world - who were totally against religion - as a result of the general freedom during the rule of the 'Abbasid Caliphs (as long as it did not interfere in the matters of state politics); the birth of philosophy in the Muslim world - which by itself gave birth to doubts and skeptical attitudes.

The First Problem:
Apparently, the first problem which was discussed and debated by the Muslims was that of predestination and free will. This was very natural, since it is a primary problem linked with human destiny and which attracts the interest of every thinking adult. Perhaps it is not possible to find a society which has reached intellectual maturity in which this problem was not raised. Secondly, the Holy Qur'an has a large number of verses on this subject, which instigate thought in regard to this problem. [3]
Accordingly, there is no reason to try to seek another source for the origin of this problem in the Islamic world.
The Orientalists, habitually, make an effort, in order to negate the originality of the Islamic teachings, to trace the roots, at any cost, of all sciences that originated amongst Muslims to the world outside the domains of Islam, in particular the Christian world. Therefore, they insist that the roots of 'ilm al-kalam should be acknowledged to lie outside Islam, and they make similar attempts with regard to the study of grammar, prosody (and perhaps semantics, rhetoric, and studies of literary and poetic devices), and Islamic 'irfan.
The problem of determinism and free will (jabr wa ikhtiyar) is the same as the problem of predestination and Divine Providence qada' wa qadar, the first formulation relates to man and his free will, while the second one relates to God. This problem also raises the issue of Divine Justice, because there is an explicit connection between determinism and injustice on the one hand, and free will and justice on the other.
The problem of justice raises the issue of the essential good and evil of actions, and the latter in its turn brings along with it the problem of the validity of reason and purely rational judgements. These problems together lead to the discussion of Divine wisdom (that is the notion that there is a judicious purpose and aim behind Divine Acts) [4], and thereby, gradually, to the debate about the unity of Divine Acts and the unity of the Attributes, as we shall explain later.
The formation of opposite camps in the debates of kalam, later acquired a great scope, and extended to many philosophical problems, such as, substance and accident, nature of indivisible particles which constitute physical bodies, the problem of space, etc. This was because, in the view of the mutakallimun, discussion of such issues was considered a prelude to the debate about theological matters, particularly those related with mabda' (primeval origin) and ma'ad (resurrection). In this way many of the problems of philosophy entered 'ilm al-kalam, and now there are many problems common to both.
If one were to study the books on kalam, specially those written after the 7th/l3th century, one would see that most of them deal with the same problems as those discussed by philosophers - especially, Muslim philosophers - in their books.
Islamic philosophy and kalam have greatly influenced each other. One of the results was that kalam raised new problems for philosophy, and philosophy helped in widening the scope of kalam, in the sense that dealing with many philosophical problems came to be considered necessary in kalam. With God's help, we hope to give an example of each of these two results of reciprocal influence between philosophy and kalam.

Al-Kalam al-'Aqli and al-Kalam al-Naqli:
Although 'ilm al-kalam is a rational and discursive discipline, it consists of two parts from the viewpoint of the preliminaries and fundamentals used by it in arguments:
(i) 'aqli (rational);
(ii) naqli (transmitted, traditional).
The 'aqli part of kalam consists of the material which is purely rational, and if there is any reference to naqli (tradition), it is for the sake of illumination and confirmation of a rational judgement. But in problems such as those related to Divine Unity, prophethood, and some issues of Resurrection, reference to naql - the Book and the Prophet's Sunnah - is not sufficient; the argument must be purely rational.
The naqli part of kalam, although it consists of issues related with the doctrines of the faith - and it is necessary to believe in them - but since these issues are subordinate to the issue of prophethood, it is enough to quote evidence from the Divine Revelation or the definite ahadith of the Prophet (S), e.g. in issues linked with imamah (of course, in the Shi'ite faith, wherein belief in imamah is considered a part of usul al-Din), and most of the issues related with the Resurrection.

Definition And Subject Matter Of 'Ilm Al-Kalam:
For a definition of 'ilm al-kalam, it is sufficient to say that, 'It is a science which studies the basic doctrines of the Islamic faith (usul al-Din). It identifies the basic doctrines and seeks to prove their validity and answers any doubts which may be cast upon them.'
In texts on logic and philosophy it is mentioned that every science has a special subject of its own, and that the various sciences are distinguished from one another due to their separate subject matter.
This is certainly true, and those sciences whose subject matter has a real unity are such. However, there is nothing wrong if we form a discipline whose unity of subject matter and the problems covered by it is an arbitrary and conventional one, in the sense that it covers diverse, mutually exclusive subjects, which are given an arbitrary unity because they serve a single purpose and objective. In sciences whose subject has an essential unity, there is no possibility of overlapping of problems. But in sciences in which there is a conventional unity among the issues dealt with, there is nothing wrong if there is an overlapping of issues. The commonness of the problems between philosophy and kalam, psychology and kalam, or sociology and kalam, is due to this reason.
Some Islamic scholars have sought to define and outline the subject matter of 'ilm al-kalam, and have expressed various opinions. But this is a mistake; because a clear-cut delineation of the subject of study is possible for only those sciences which have an essential unity among the problems dealt with. But in those sciences in which there is a conventional unity of problems dealt with, there can be no unity of subject. Here we cannot discuss this issue further.

The Name "'Ilm al-Kalam":
Another point is why this discipline has been called " 'ilm al-kalam", and when this name was given to it. Some have said that it was called "kalam" (lit. speech) because it gives an added power of speech and argument to one who is well-versed in it. Some say that the reason lies in the habit of the experts of this science who began their own statements in their books with the expression "al-kalamu fi kadha". Others explain that it was called "kalam" because it discussed issues regarding which the Ahl al-Hadith preferred to maintain complete silence.
Yet according to others this name came to be in vogue when the issue whether the Holy Qur'an (called "kalamullahi") ,the Divine Utterance [5], i.e. the Holy Qur'an) is created (makhluq) or not, became a matter for hot debate amongst the Muslim - a controversy which led to animosity between the two opposite camps and bloodshed of many. This is also the reason why that period is remembered as a "time of severe hardship" - mihnah.
That is, since most of the debates about the doctrines of the faith revolved around the huduth (createdness, temporality) or the qidam (pre-eternity) of the "Utterance" or kalam of God, this discipline which discussed the principal doctrines of the faith came to be called " 'ilm al-kalam" (lit. the science of the Utterance). These are the various opinions that have been expressed about the reason why 'ilm al-kalam was given this name.

The Various Schools of Kalam:
The Muslims differed with one another in matters of the Law (fiqh), following differing paths and dividing into various sects, such as Ja'fari, Zaydi, Hanafi, Shafi'i, Maliki and Hanbali, each of which has a fiqh of its own. Similarly, from the viewpoint of the doctrine, they divided into various schools, each with its own set of principal doctrines. The most important of these schools are: the Shi'ah, the Mu'tazilah, the 'Asha'irah, and the Murji'ah.
Here it is possible that the question may arise as to the reason behind such regretful division of the Muslims into sects in matters dealing with kalam and fiqh, and why they could not maintain their unity in these spheres. The difference in matters of kalam causes disunity in their Islamic outlook, and the disagreement in the matter of fiqh deprives them of the unity of action.
Both this question and the regret are justified. But it is necessary to pay attention to the two following points:
(i) The disagreement in issues of fiqh among the Muslims is not so great as to shatter the foundations of the unity of doctrinal outlook and mode of practice. There is so much common in their doctrinal and practical matters that the points of difference can hardly inflict any serious blow.
(ii) Theoretical differences and divergence of views is inevitable in societies in spite of their unity and agreement in principles, and as long as the roots of the differences lie in methods of inference, and not in vested interests, they are even beneficial; because they cause mobility, dynamism, discussion, curiosity, and progress. Only when the differences are accompanied by prejudices and emotional and illogical alignments, and lead individuals to slander, defame, and treat one another with contempt, instead of motivating them to endeavour towards reforming themselves, that they are a cause of misfortune.
In the Shi'ite faith, the people are obliged to imitate a living mujtahid, and the mujtahidun are obliged to independently ponder the issues and form their independent opinions and not to be content with what has been handed down by the ancestors. Ijtihad and independence of thought inherently lead to difference of views; but this divergence of opinions has given life and dynamism to the Shi'ite fiqh. Therefore, difference in itself cannot be condemned. What is condemnable is the difference which originates in evil intentions and selfish interests, or when it centres around issues which drive Muslims on separate paths, such as the issue of imamah and leadership, not the difference in secondary and non-basic matters.
To undertake an examination of the intellectual history of the Muslims so as to find which differences originated in evil intentions, vested interests, and prejudices, and which were a natural product of their intellectual life, whether all points of difference in the sphere of kalam should be regarded as fundamental, or whether all problems in fiqh should be regarded as secondary, or if it is possible that a difference in kalam may not be of fundamental significance whereas one in fiqh may have such importance - these are questions which lie outside the brief scope of this lecture.
Before we take up the schools of kalam for discussion, it is essential to point out that there has been a group of scholars in the Islamic world which was basically opposed to the very idea of 'ilm al-kalam and rational debate about Islamic doctrines, considering it a taboo and an innovation in the faith (bid'ah). They are known as "Ahl al-Hadith." Ahmad ibn Hanbal, one of the imams of jurisprudence of the Ahl al-Sunnah, stands foremost among them.
The Hanbalis are totally against kalam, Mu'tazilite or Ash'arite, not to speak of the Shi'ite kalam. In fact they are basically opposed to logic and philosophy. Ibn Taymiyyah, who was one of the eminent scholars of the Sunni world, gave a verdict declaring kalam and logic as 'unlawful'. Jalal al-Din al-Suyuti, another figure among the Ahl al-Hadith, has written a book called Sawn al-mantiq wa al-kalam 'an al-mantiq wa al-kalam ("Protecting speech and logic from [the evil of] 'ilm al-kalam and the science of logic").
Malik ibn Anas is another Sunni imam who considers any debate or inquiry about doctrinal matters to be unlawful. We have explained the Shi'ite viewpoint in this matter, in the introduction to Vol.V of Usul-e falsafeh wa rawish-e riyalism. [6]
The important schools of kalam, as mentioned earlier, are: Shi'ah, Mu'tazilah, Asha'irah, and Murji'ah. Some sects of the Khawarij and the Batinis, such as the Isma'ilis, have also been considered as schools of Islamic kalam. [7]
However, in my view, none of these two sects can be considered as belonging to the schools of Islamic kalam. The Khawarij, although they held specific beliefs in the matters of doctrine, and perhaps were the first to raise doctrinal problems by expressing certain beliefs about Imamah, the kufr (apostasy) of the fasiq (evil-doer, one who commits major sins), and considered the disbelievers in these beliefs as apostates, but they did not, firstly, create a rationalist school of thought in the Muslim world, and, secondly, their thinking was so much deviated - from the viewpoint of the Shi'ites - that it is difficult to count them among Muslims. What makes things easy is that the Khawarij ultimately became extinct and only one of their sects, called "Abadiyyah" has some followers today. The Abadiyyah were the most moderate of all the Khawarij, and that is the reason why they have survived until today.
The Batinis, too, have so much liberally interfered in Islamic ideas on the basis of esotericism that it is possible to say that they have twisted Islam out of its shape, and that is the reason why the Muslim world is not ready to consider them as one of the sects of Islam.
About thirty years ago when the Dar al-Taqrib Bayna al-Madhahib al-'Islamiyyah was established in Cairo, the Imamiyyah Shi'ah, the Zaydiyyah, the Hanafi, the Shafi'i, the Maliki and the Hanbali sects, each of them had a representative. The Isma'ilis tried hard to send a representative of their own; but it was not accepted by other Muslims. Contrary to the Khawarij, who did not create a system of thought, the Batinis, despite their serious deviations, do have a significant school of kalam and philosophy. There have emerged among them important thinkers who have left behind a considerable number of works. Lately, the Orientalists have been showering great attention on the Batini thought and works.
One of the prominent Isma'ili figures is Nasir Khusrow al-'Alawi (d. 841/1437-38), the well-known Persian poet and the author of such famous works as Jami' al-hikmatayn, Kitab wajh al-Din, and Khuwan al-'ikwan. Another is Abu Hatam al-Razi (d. 332/943-44), the author of A'lam al-nubuwwah. Others are: Abu Ya'qub al-Sijistani, the author of Kashf al-mahjub (its Persian translation has been recently published), who died during the second half of the 4th/l0th century; Hamid al-Din al-Kirmani, a pupil of Abu Ya'qub al-Sijistani, has written a large number of books about the Isma'ili faith; Abu Hanifah Nu'man ibn Thabit, well-known as Qadi Nu'man or "the Shi'ite Abu Hanifah" (i.e. Isma'ili); his knowledge of fiqh and hadith is good, and his well-known book Da'a'im al-'Islam has been printed by lithotype several years ago.

Mu'tazilah:
We shall begin our discussion - and we shall explain later why - with the Mu'tazilah. The emergence of this sect took place during the latter part of the first century or at the beginning of the second. Obviously 'ilm al-kalam, like any other field of study, developed gradually and slowly attained maturity.
First we shall enumerate the principal Mu'tazilite beliefs, or what is better to say, the basic and salient points of their school of thought. Second, we shall point out the well-known Mu'tazilite figures and speak of their fate in history. Then we shall give an account of the main outlines of the transitions and changes in their thought and beliefs.
The opinions held by the Mu'tazilah are many, and are not confined to the religious matters, or which according to them form an essential part of the faith. They cover a number of physical, social, anthropological and philosophical issues, which are not directly related with the faith. However, there is a certain relevance of these problems to religion, and, in the belief of the Mu'tazilah, any inquiry about the matters of religion is not possible without studying them.
There are five principal doctrines which, according to the Mu'tazilah themselves, constitute their basic tenets:
(i) Tawhid, i.e. absence of plurality and attributes.
(ii) Justice ('adl), i.e. God is just and that He does not oppress His creatures.
(iii) Divine retribution (at-wa'd wa al-wa'id), i.e. God has determined a reward for the obedient and a punishment for the disobedient, and there can be no uncertainty about it. Therefore, Divine pardon is only possible if the sinner repents, for forgiveness without repentance (tawbah) is not possible.
(iv) Manzilah bayna al-manzilatayn (a position between the two positions). This means that a fasiq (i.e. one who commits one of the "greater sins," such as a wine imbiber, adulterer, or a liar etc.) is neither a believer (mu'min) nor an infidel (kafir); fisq is an intermediary state between belief and infidelity.
(v) al-'amr bil ma'ruf wa al-nahy 'an al-munkar [bidding to do what is right and lawful, and forbidding what is wrong and unlawful]. The opinion of the Mu'tazilah about this Islamic duty is, firstly, that the Shari'ah is not the exclusive means of identifying the ma'ruf and the munkar; human reason can, at least partially, independently identify the various kinds of ma'ruf and munkar. Secondly, the implementation of this duty does not necessitate the presence of the Imam, and is a universal obligation of all Muslims, whether the Imam or leader is present or not. Only some categories of it are the obligation of the Imam or ruler of Muslims, such as, implementation of the punishments (hudud) prescribed by the Shari'ah, guarding of the frontiers of Islamic countries, and other such matters relating to the Islamic government.
Occasionally, the Mu'tazilite mutakallmun have devoted independent volumes to discussion of their five doctrines, such as the famous al-'Usul al-khamsah of al-Qadi 'Abd al-Jabbar al-'Astarabadi (d. 415/ 1025), a Mu'tazilite contemporary of al-Sayyid al-Murtada 'Alam al-Huda and al-Sahib ibn 'Abbad (d. 385/995).
As can be noticed, only the principles of tawhid and Justice can be considered as parts of the essential doctrine. The other three principles are only significant because they characterize the Mu'tazilah. Even Divine Justice - although its notion is definitely supported by the Qur'an, and belief in it is a necessary part of the Islamic faith and doctrine - has been made one of the five major doctrines because it characterizes the Mu'tazilah. Or otherwise belief in Divine Knowledge and Power is as much an essential part of the Islamic faith and principal doctrine.
Also in the Shi'ite faith the principle of Divine Justice is considered one of the five essential doctrines. It is natural that the question should arise: what is particular about Divine Justice that it should be counted.among the essential doctrines, though justice is only one of the Divine Attributes? Is not God Just in the same manner as He is the Omniscient, the Mighty, the Living, the Perceiver, the Hearer and the Seer? All those Divine Attributes are essential to the faith. Then why justice is given so much prominence among the Divine Attributes?
The answer is that Justice has no advantage over other Attributes. The Shi'ite mutakallimun have specially mentioned justice among the principal Shi'ite doctrines because the Ash'arites - who form the majority of the Ahl al-Sunnah - implicitly deny that it is an Attribute, whereas they do not reject the Attributes of Knowledge, Life, Will, etc. Accordingly, justice is counted among the specific doctrines of the Shi'ah, as also of the Mu'tazilah. The above-mentioned five doctrines constitute the basic position of the Mu'tazilah from the viewpoint of kalam, otherwise, as said before, the Mu'tazilite beliefs are not confined to these five and cover a broad scope ranging from theology, physics and sociology to anthropology, in all of which they hold specific beliefs, a discussion of which lies outside the scope of these lectures.

The Doctrine of al-Tawhid:
Beginning with tawhid it has various kinds and levels: al-tawhid al-dhati (Unity of the Essence), al-tawhid al-sifati (Unity of the Attributes, i.e., with the Essence), al-tawhid al-'af'ali (Unity of the Acts), al-tawhid al-'ibadi (monotheism in worship).
Al-Tawhid al-dhati: It means that the Divine Essence is one and unique; it does not have a like or match. All other beings are God's creations and inferior to Him in station and in degree of perfection. In fact, they cannot be compared with Him. The idea of al-tawhid al-dhati is made clear by the following two [Qur'anic] verses:
Nothing is like Him. (42:11)
He does not have a match [whatsoever]. (112:4)
AI-Tawhid al-sifati: It means that the Divine Attributes such as Knowledge, Power, Life, Will, Perception, Hearing, Vision, etc. are not realities separate from God's Essence. They are identical with the Essence, in the sense that the Divine Essence is such that the Attributes are true of It, or is such that It manifests these Attributes.
Al-Tawhid al-'af'ali: It means that all beings, or rather all acts [even human acts] exist by the Will of God, and are in some way willed by His sacred Essence.
Al-Tawhid al-'ibadi: It means that except God no other being deserves worship and devotion. Worship of anything besides God is shirk and puts the worshipper outside the limits of Islamic tawhid or monotheism.
In a sense al-tawhid al-'ibadi (tawhid in worship) is different from other kinds of tawhidi, because the first three relate to God and this kind relates to the creatures. In other words, the Unity of Divine Essence, His Uniqueness and the identity of the Essence and Attributes, the unity of the origin of everything - all of them are matters which relate to God. But tawhid in worship, i.e. the necessity of worshipping the One God, relates to the behaviour of the creatures. But in reality, tawhid in worship is also related to God, because it means Uniqueness of God as the only deserving object of worship, and that He is in truth the One Deity Worthy of Worship. The statement "la ilaha illallah" encompasses all aspects of tawhid, although its first signification is monotheism in worship.
Al-tawhid al-dhati and al-tawhid al-'ibadi are part of the basic doctrines of Islam. It means that if there is a shortcoming in one's belief in these two principles, it would put one outside the pale of Islam. No Muslim has opposed these two basic beliefs.
Lately, the Wahhabis, who are the followers of Muhammad ibn 'Abd al-Wahhab, who was a follower of Ibn Taymiyyah, a Hanbali from Syria, have claimed that some common beliefs of the Muslims such as one in intercession (shafa'ah) and some of their practices such as invoking the assistance of the prophets (A) and holy saints (R) are opposed to the doctrine of al-tawhid al-'ibadi. But these are not considered by other Muslims to conflict with al-tawhid al-'ibadi. The point of difference between the Wahhabis and other Muslims is not whether any one besides God - such as the prophets or saints - is worthy of worship. There is no debate that anyone except God cannot be worshipped. The debate is about whether invoking of intercession and assistance can be considered a form of worship or not. Therefore, the difference is only secondary, not a primary one. Islamic scholars have rejected the viewpoint of the Wahhabis in elaborate, well-reasoned answers.
Al-tawhid al-sifati (the Unity of Divine Essence and Attributes) is a point of debate between the Mu'tazilah and the Asha'irah. The latter deny it while the former affirm it. Al-tawhid al-'af'ali is also another point of difference between them, with the difference, however, that the matter is reverse; i.e. the Asha'irah affirm it and the Mu'tazilah deny it.
When the Mu'tazilah call themselves "ahl al-tawhid", and count it among their doctrines, thereby they mean by it al-tawhid al-sifati, not al-tawhid al-dhati, nor al-tawhid al-'ibadi (which are not disputed), nor al-tawhid al-'af'ali. Because, firstly, al-tawhid al-'af'ali is negated by them, and, secondly, they expound their own viewpoint about it under the doctrine of justice, their second article.
The Asha'irah and the Mu'tazilah formed two radically opposed camps on the issues of al-tawhid al-sifati and al-tawhid al-'af'ali. To repeat, the Mu'tazilah affirm al-tawhid al-sifati and reject al-tawhid al-'af'ali, while the Ash'arite position is the reverse. Each of them have advanced arguments in support of their positions.

Source: Shia