1. The notion of 'wahdat al-wujud' [Unity of Being] is a monistic understanding of tawheed, the doctrine of oneness of God. It is considered one of the most fundamental concepts in mysticism and in mystical schools especially that of Ibn Arabi. According to this principle, existence [wujud] is a single and eternal reality which is no one other than God. No one other God has real existence. Whatever comes to our sight are in reality various expressions of that single reality that have manifested in the form of things which are, in fact, the outward radiance of that One Being.
2. There are also some philosophical argument regarding unity of being though it is an argument that can be proved only through intellectual intuition. This argument is based on the “principiality of existence” and “conceptual commonality of existence”. Among the arguments put forth in this regard is that existence, in view of commonality of the concept of existence, should have a single reality because it is not possible to extract a single concept from different realities. As well, in order to reaffirm the notion of unity of being, they have resorted to the principle of “the truth in its simplicity is all things” ["بسيط الحقيقه كل الاشياء"].
3. There have been some jurisprudents and theologians who have trenchantly opposed the notion of unity of being with some of them considering it tantamount to shirk (polytheism). According to them, God is separated from things because the purity of God’s existence is not combinable with material existents.
4. It seems that the reason why some Muslim scholars have strongly opposed mystics and the notion of unity of being is the profundity or the complexity of the points raised in mysticism regarding the said notion. Meanwhile, some of those who claim to be mystics have failed to explain this concept in a proper way and a few others have not been able to comprehend and understand this precise notion because of their own incompetence and weakness.
5. Mulla Sadra being a philosopher as well as a mystic endeavored to clarify the meaning of the unity of being. He also struggled to do away with the spurious arguments and misgivings which were due, largely, to misunderstanding. For example, in his Asfar Arba’ah (The Four Journeys) Mulla Sadra differentiates between pure and unfolded (munbasit) beings. The former is unlimited and absolute such as the existence of the One God and the latter is distributed among contingent or possible images (hayakil). When gnostics speak of unity of being and absolute being, they refer to the first meaning not the second one. This confusion between pure and unfolded existence has led some scholars to err about the notion or deny it or even excommunicate others.
The notion of 'wahdat al-wujud' [Unity of Being] is a monistic understanding of tawheed, the doctrine of oneness of God. It is considered one of the most fundamental concepts in mysticism and in mystical schools especially that of Ibn Arabi. According to this principle, existence [wujud] is a single and eternal reality which is none other than God. No one other God has real existence. Whatever comes to our sight are in reality various expressions of that single reality that have manifested in the form of things which are, in fact, the outward radiance of that One Being.
Therefore, we cannot divide being (wujud) into creator and created. Hence, we must believe in one real being that is God. He, the Exalted, sometimes descends and becomes like creatures.
Ibn Arabi says:
"فما وصفناه بوصف الاّ كنّا نحن ذلك الوصف، فوجودنا وجوده، ونحن مفتقر اليه من حيث وجودنا، و هو مفتقر الينا من حيث ظهوره لنفسه."
Translation: Whatever we speak of Him, We have in reality described ourselves and spoken of ourselves because our existence is His existence. We are in need of Him for our existence and He needs us to express Himself.”
According to Ibn Arabi, God and creatures aren’t but one thing and they are in need of each other because they are the image of one reality. In fact, the creatures are not but the attributes and qualities of the Truth. However, the relationship between existence and God is a real relationship where the relationship between existence and creatures is figurative.
It is said in Futuhaat Makkiyah about “confusion”: The difference between confusion of ‘the people of God’ and ‘people of thought’: The men of wisdom say:
و فى كل شى له آية
تدل على انه واحد،
“There is a sign of Him in everything indicating that He is One.”
But the people of manifestation (tajalli) say:
و فى كل شىء له آية
تدل على انه عينه
There is a sign of Him in everything indicating that He is the same as that.”
The fact is that there is none in the world of existence other than God and no one knows God except God Himself. Perhaps, it is for the same reason that people like Abu Yazid have said “I am Allah” and also those before him who have said “Glorified I am”.
Finally, the most unequivocal statement by Ibn Arabi regarding unity of being and which has been criticized a lot are the following passage and poem in his , al-Fotuhat al-Makkiyah:
فسبحان من اظهر الاشياء و هو عينها
That is, purified and glorified is He Who made things appear and He is the same as those things.
فما نظرت عينى الى غير وجهه
و ما سمعت اذنى خلاف كلامه
فكل وجود كان فيه وجوده
و كل شخيص لم يزل فى منامه
That is, my eyes do not see anything but Him, and ears do not hear anything but His speech; hence everything exists in Him and everything rests in His restful place.
Unity of being (wahdat al-wujud) being the basic axis of gnostic schools and religion means that every being which is seen in the world is nothing but the theophanies [tajalliyat] or Self-manifestation of God. It is incorrect to say that these are His creatures. In fact, these are not but Him. That is to say, instead of telling:
“I love the entire universe because the entire universe is His”, we must say “I love the entire universe because the entire is him.” As Shaykh Mahmood Shabistari, one of the eighth century gnostics has said:
جناب حضرت حق را “دويى” نيست
در آن حضرت من و ما و تويى نيست
من و ما و تو و او هست يك چيز
كه در وحدت نباشد هيچ تمييز
شود با وجه باقى، غير هالك
يكى گردد سلوك و سير و سالك
The Truth is not but One; You, we and I are not but One, we, I, thou and He is not but one thing; There is no division in unity; The face of Truth is Lasting, others are wayfarers.
Imam Muhammad Ghazzali says: “Gnostics have flown to the pinnacle of truth from the bottom of figurativeness and after acquiring perfection, they themselves see clearly through this ascension that there is none in the realm of existence except God. All except God does perish. Not only at every time but eternally and permanently, everything has two faces, one towards the self, the other towards God. He is non-existent in terms of the first face. The conclusion is that there is no existent other than God and His face. كل شى هالك الاّ وجهه" ازلاً و ابداً.
For this reason, gnostics do not need to wait until the Day of Judgment in order to hear the call “Whose then will be the kingdom? – God's, the One, the Omnipotent.” In fact, this call never stops reverberating in their ears. They never understand from “Allahu Akbar” He is Greater than all others. That is never the case because there is no one in the realm of existence other than Him. So such a comparison is wrong; others cannot be in the company of Truth.
It is necessary to note that the term “principiality of existence” is not seen in Mohyiddin ibn Arabi’s writings and words and such a term was not commonplace before him either. In fact, those who came later and embarked on explaining Ibn Arabi’s works and those of other mystics were inspired by Ibn Arabi’s teachings and began to use such terms.
Arguments on Unity of Being:
Philosopher-gnostics like Mulla Sadra and others have presented philosophical arguments which are based on the principiality of existence and conceptual commonality. Among the arguments mentioned is the following: Keeping in view the conceptual commonality of existence, existence must be a single reality because extracting a single meaning from different realities is not possible.
And also, among the principles reaffirming the notion of unity of being in philosophy is “the truth in its simplicity is all things”. That is to say, if the essence of simple (non-composite) truth did not include some realities, the simple truth would be compound, though by way of consideration, and combination is inconsistent with simplicity and abstractness. Hence, absolute truth incorporates and has the perfections of the entities in a simple (non-compsite) way.
Jurists’ and Theologians’ argument in rejection of the notion of unity:
Some jurisprudents and theologians, whether Shia or Sunni or even some Christian theologians, have criticized Sufi and gnostic beliefs especially the notion of unity of being. Some have even excommunicated gnostics for holding such beliefs because they believed that such an idea is opposed to divine teaching. For example, the motto “there is no god but Allah” which is the first motto in Islam is opposed to “there is no existent (being) except Allah”. Because the first statement tells us not to worship and praise anything other than Allah e.g. idols, deities and objects but the second motto says that everything including the idols and deities are God and there is basically nothing other than God. In fact, it is God Who is worshipped in different ways and manners.
They have criticized what mystics have said: "سبحان من اظهر الاشياء و هو عينها" Glorified is He who made things manifest yet He is not but the same things. They have criticized mystics saying: ‘how can God be the same as the entities whereas some of them are mean, dirty, contaminated and impure? Such a statement amounts to infidelity (kufr).’
It should be noted that some gnostics have failed to explain their intention clearly and it is likely that some critics have not understood the mystics’ comments and statements properly and this has led them to object and criticize or even pass improper judgments about mystics in general and Ibn Arabi in particular. The discussion concerning unity of being is very difficult and precise. Not everyone can give a thorough explanation of it nor can he comprehend it.
Mulla Sadra is one of those philosophers and gnostics who endeavored to give a complete analysis of the notion of unity of being so as to prevent misconceptions and erroneous interpretations.
When it comes to how the reality of existence (haqiqat-i wujud) infiltrates definite beings and particular realities, Mulla Sadra says:
You should know that the reality of existence has three levels: The first level contains “existence” (wujud) itself and has no relation to anything other than itself. From a theological point of view this existence is God, Who is absolute and distinct from and higher than His creation. According to this view God is the absolute light (nur-i mutlaq) and for this reason is hidden from human intellect.
The second level pertains to the “unfolded existence” (wujud-i munbasit). Existence at this level is still pure, meaning that it is still simple or unfolded and a single truth (haqiqat-i wahid). But apart from this, it has the potential of effusion to all directions. From a theological point of view, it is the basis of the appearance and the manifestation of God.
The second level relates to “particular existences” (wujudat-i khas). These things are the stages and the levels of the realization of the “unfolded existence”. At each of these levels, when human intellect considers existence as an independent entity in relation to itself, it changes itself into quiddity. However, if quiddities that are formed in this way are compared to the “unfolded existence” (wujud-i munabasit), they are mere shadows.
The third level pertains to the “unfolded existence” (wujud-i munbasit). Existence at this level is still pure, meaning that it is still simple or unfolded and a single truth (haqiqat-i wahid). But apart from this, it has the potential of effusion to all directions. From a theological point of view, it is the basis of the appearance and the manifestation of God.
A man of knowledge and wisdom can discern the reality of being and its absoluteness at one glance and at the next glance he can see different and variant things. He will see the truth behind the veil of variant things and realize that it is the “pure existence” (wujud-i mahd) and the “simple (non-composite) identity” (huwiyyat-i basitah), which has by no means any trace or sign of multiplicity (kithrat). The reality of existence in this sense is “one” (wahid) with the “absolute unity” and is free from “absoluteness” (atlaq) and “determination” (taqyyid). The reality of existence encompasses all levels and signs.
Thereupon, he further adds to repel a misgiving:
It is proved that when the Necessary Truth is referred to as Absolute Truth (wajib-e mutlaq), they refer to existence in the first meaning, the abstract reality not the third and last meaning, or else the individual will be led astray as a result of not distinguishing between the two meanings. He will end up being an atheist, a permissive or someone who would believe that possible beings, which are imperfect, can be characteristic of divine attributes. 
Else where Mulla Sadra discussing under the title “illusion and awakening” says:
Some so called Sufis or imitators who have not covered the path of gnostics and have not reached the rank of gnostics have, due to intellectual inability, ideological weakness and influence of illusion, thought that that Single Being who is described by gnostics as One and “Without Quiddity” and the “Invisible of the Invisibles” cannot practically materialize or manifest independently of theophanies and expressions. Rather what materializes is the realm of form and its spiritual and sensual powers and “Allah” is the Apparent of all, not a reality apart from them. And that Apparent of all is the reality of the major human being and the tangible Book, and this minor human being is a diminutive copy of that. This saying and belief is disbelief and pure heresy. Whoever has little knowledge and understanding will not utter such a thing. It is a slander and pure accusation to ascribe such a belief to Sufi veterans and their leaders. Their mind and conscience are pure from such words and it is likely that the cause of such ignorant conjectures could be a mistake in the application of the term of absolute existence which is sometimes applicable to the Truth and sometimes to absolute inclusiveness and sometimes to absolute rational generality.
It is appropriate to give an example of the difference between gnostics and other scholars due to misinterpretation or insufficiency of explanation or misunderstanding:
One of the books authored in rejection of gnosticism and mysticism is titled “Mesra’ al-Tasawuf” by Burhanuddin Burqaei (888 – 809 A.H.). In that book, instances of such misconceptions have been mentioned, one of which is the following:
Shaykh Zaynuddin Abdur Rahim bin Al-Hasan Iraqi, whom Buaqaei calls Shaykh Al-Shuyukh, Shaykhul Islam and Memorizer of the Age says, about Ibn Arabi:
So these opponent of God, the Messenger of God and all believers came and endorsed the work of the Sufi school considering them to be among theologians and said: “In reality, gnostic is one who not only sees the truth in everything; but he also considers the truth to be the same as those things. Undoubtedly, he who says this is more polytheist than Jews and Christians. Because a Jew or a Christian may have worshipped a close servant of God and this Ibn Arabi considers worshipping a calf to be worship of God. In fact, his saying amounts to considering god to be the same as dog, pig, etc. and even the same as dirt. One of the knowledgeable scholars told me that he saw one of the followers of this cult in Alexandria who told him that God is the same as everything. A donkey was passing and I asked him: And this donkey also?! He answered: “Yes, this donkey and its stool!” I said: “This stool?!!” He said: “Yes, the stool also!! and ….”
In the West also, mystics’ view concerning mystical notions has been criticized owing, largely, to misconceptions. The notion of unity of being has been particularly the source of these objections.
Dr. Barnes, Birmingham bishop says: “In my view, all kinds of unity of being should be rejected because if man is really a part of God, the evil and impurity which are in man’s nature should also be in God.”
Stace, a Christian theologian writes about the problem of the notion of unity of being as such:
“Apparently, we can find three main reasons for believers and monotheists’ pessimism towards unity of being. First, monotheism believes in a personified or personal God whereas Western thinkers believe in absolute non-personification.
Second, if, according to the notion of unity of being, the world and everything in it are godly, then in that case evil will also be godly.
Third, there is a strong feeling and also a staunch belief in all religion about God’s glory and omnipotence. This feeling is equal to the image that Rudolf Otto has of awe and solemnity. Mankind is nothing when compared to God. He is a sinful creature with barriers between him and God. He is impure and unforgiven. He is worthy of being called unjust and ignorant. Having said that , it is slanderous and heretic to claim that we are united with God in the sense of being one with Him. The difference between God and man and between God and the Universe is poles apart.
It is, therefore, becoming clear why theologians and jurisprudents – Muslims and non-Muslims – are opposed to the notion of unity of being. It became clear that it is because of the profundity and ambiguity of the notion or the improper explanation of some claimants of mysticism and the complexity of the concept that many scholars have rejected the notion. The correct thing to do is not to tell anything regarding such concepts about which one lacks information. It is not good to accuse gnostics of heresy and atheism when one has not understood them properly. It is fair to say that he does not know anything rather than to excommunicate someone or consider him hypocrite.
 Mohyiddin Ibn Arabi, Fusuz al-Hekam p. 164.
 Mohyiddin Ibn Arabi, al-Fotuhat al-Makkiyah fi Asrar al-Malekiyah wa al-Makkiyah, vol.1, p. 272, chap.50.
 Al-Futuhat al-Makkiyah, vol.2, p. 459.
 Shaykh Mahmood Shabistari, Gulshan Raz.
 Muhammad Ghazzali, Mishkatul Anwar, p. 150 – 152.
 Sayyid Yahya Yathrebi, Falsafa-e Irfan, pp. 127 – 128, Islamic Propagations Office of the Islamic Seminary of Qom, third edition, 1374 (1995).
 Mulla Sadra, al-Asfar al-arba'ah, vol. 1, p. 262.
 Ibid, p. 330.
 Bertrand Russell, Knowledge and Religion, p. 127, cited from the Philosophy of Mysticism, p. 173.
 Mysticism and Philosophy, p. 256, narrated by Sayyid Yahya Yathrebi, Philosophy of Mysticism, p. 173.