The famous Arabic linguist Ibn Faaris defines it as ‘…to add or append, not being single or one.’
Ar-Raaghib al-Asbahani (d. 425 AH) said “Shirk is defined as affirming partners with Allaah.”
Ibn Mas’ood asked the Prophet (sallallaahu alayhi wassallam) “What is the greatest sin?” he replied “To take alongside Allaah a partner (nidd) even though it was He that created you.” (al-Bukhari and Muslim)
The jaahiliyyah Arabs believed in Allaah, and that He created everything, and gives life and death, yet this did not cause them to enter Islaam.
The people whom the prophet was sent to worshipped different objects. Some worshipped idols and stones, whereas others worshipped angels and prophets. Yet the Prophet did not distinguish between these people and considered them all equal in their disbelief.
The reason these people worshipped other objects was that they desired these objects to intercede on their behalves with Allaah. They said that they have a high status and thus, by pleasing them, they would in turn please Allaah.
The Prophet was sent to mankind in order that people worship Allaah alone. He was not sent so that he be worshipped besides Allaah, or that people turn to saints and graves in order that they be venerated.
The Prophet (sallallaahu alayhi wassallam) prohibited building mosques over graves, as this is one of the primary methods through which shirk is sanctioned. Once Umm Salamah mentioned the beautiful churches she had seen in Ethiopia. The Prophet said, “whenever a pious person died amongst them, they would build places of worship over their graves and carve images. Such people are the worst of mankind in the sight of Allaah.” (Bukhari and Muslim)
He also forbade burying the dead inside mosques, for it too is one of the primary ways that leads to shirk . He prayed on his deathbed: “O Allaah! Do not make my grave an idol that is worshipped.” (Muwatta’)
He forbade worshipping Allaah at places where shirk occurs.
The Prophet also prohibited the Muslims from excessively praising him, as this is one of the ways to shirk .
He (sallallaahu alayhi wassallam) said: “Do not excessively praise me as the Christians did with Jesus the Son of Mary. Rather, I am only the slave of Allaah and His messenger.” (Bukhari and Muslim)
The Prophet also forbade image-making, which is how shirk began in history. Thus by stopping this, he (sallallaahu alayhi wassallam) blocked one of the paths to shirk . The most severely punished on the Day of Judgement will be those who tried to imitate Allaah’s creation. (Bukhari)
The Prophet (sallallaahu alayhi wassallam) commanded the companions to level all graves (which are raised with monuments built on them) and destroy images that they came across. Ali ibn Abi Taalib told Abu’l-Hayyaj al-Asadi to do this. (Saheeh Muslim).
During the Battle of Hunayn when some of the new Muslims wanted a ‘Dhaat Anwaat’ as the mushriks had one.
“ Shirk is to make du’a to other than Allaah in matters in which only Allaah should be asked, or to believe that a certain object has powers that only Allaah has, or to intend to please an object with an act that should only be done for Allaah.”
To claim that any created object knows everything, or can hear any plea directed to it, is shirk . Whenever any specific right of Allaah is given to any other object, whether that object be a living being or an inanimate object, real or imagined, shirk has taken place.
Human beings were created upon the pure worship of Allaah, before they deviated into the practice of shirk and there are many proofs for this. Allaah created humans with a natural inclination ( fitrah ) which is ingrained in everyone, and guides people about right and wrong.
It is due to this that all peoples know that murder, lying an stealing are evil actions and that looking after people, being kind to parents are good acts. This fitrah was placed in every single person at the time of Adam’s creation. When Allaah created Adam and the progeny of Adam, He made a covenant with them. The covenant is known as the mithaaq in Arabic, and it specified that only Allaah is the true Lord deserving of worship.
“ And mention when your Lord took from the children of Adam – from their loins – their descendents and made them testify of themselves, (saying to them), “Am I not your Lord?” They said “Yes, we have testified.” (This) – lest you should say on the day of Resurrection, “Indeed, we were of this unaware.”
The mithaaq is referred to in the hadeeth where the Prophet (sallallaahu alayhi wassallam) narrated that Allaah said: “ I have created My servants, all of them, pure (and inclined towards worship), but the Shayaateen came and diverted them from the religion. They prohibited them from matters that I allowed and commanded them to associate partners with Me…” (Saheeh Muslim).
The mithaaq is ingrained into the subconscious of human beings, even though they do not remember it. Allaah’s prophets delivered the message of the pure worship of Allaah, which is in the fitrah . So when a person hears the prophet’s message, she/he becomes inclined towards it, as it conforms with her/his natural way.
The Prophet (sallallaahu alayhi wassallam) said: “Every child is born upon the fitrah; then his parents make him a Jew or a Christian.” (Bukhaaree)
Ibn Qayyim (raheemahullaah) wrote: “The fitrah is open to knowledge of Islaam and the love of Islaam. The fitrah necessitates acknowledgement and love (of Allaah)…so every single child is born in a state in which he or she acknowledges the Lordship (of Allaah). So if the child were left without any preventive factors, he would not turn away from the fitrah to anything else.” (Shifaa al-’Aleel).
The distinguished scholar of hadeeth Shaykh Muhammad Naasiruddeen al-Albaanee ( raheemahullaah) stated “It is established in Islaam and the Sharee’ah that mankind in the beginning was a single nation upon true tawheed then shirk gradually overcame them. The basis for this is the saying of Allaah,
“ Mankind was one Ummah then Allah sent the Prophets as bringers of good tidings and warners”
Ibn Abbaas, may Allaah be pleased with him , said “between Prophet Nooh (Noah) and Aadam, peace be upon them both, were ten generations, all of them were upon the Sharee’ah of truth, but then they differed. So Allaah sent Prophets to bring good news and also warn their people.”
Shaykh al-Albaanee then went on to say that this refutes the philosophers and atheists who claim that the natural basis of man is Shirk , and that Tawheed evolved in man!
Religion began with humanity worshipping the forces of nature due to their amazement at the cataclysmic and devastating effects of their environments and the natural world. Thus, thunder, lightening, earthquakes, volcanoes etc were believed to be conceived of supernatural beings. Thus, humans sought ways to appease the beings through rites, rituals, prayers and sacrifices.
The native North Americans, who believe in spirits of the river and of the forest, are used as examples of this early stage in the evolution of religion, known as Animism. Eventually Diathesis emerged in which all of the supernatural powers were confined in two main gods, usually a god of good and a god of evil.
According to the evolutionists, an example of this stage can be seen in the religion of the Zoroastrians of Persia. When tribes gave way to nations, tribal gods in turn gave way to a national god and monotheism was supposedly born. Thus, according to this view, monotheism has no divine origin.
The evidence which proves that humanity’s monotheistic concept of One God degenerated into idol-worship, man-worship, saint worship, and minor gods is extensive. Islaam believes that humans beings started out as worshipping God alone then after deviated into various forms of polytheism as have just been mentioned. Islaam holds that God sent Messengers to all the tribes and nations of the Earth to guide them back to the path of monotheism.
Thus, we find amongst all of the so-called primitive tribes that have been discovered, the belief in One Supreme God. The central America Mayans believe in One God who created everything, whom they call ‘Itzamna,’  the Mende peoples of Sierra Leone in West Africa believe in One God who created the universe and spirits who they call ‘Ngewo,’   John Hinnels, Dictionary of Religions (Penguin Books: 1884), p. 93
in the ancient Babylon the main deity of the city, ‘Marduk,’  was seen as the Supreme God. In Hinduism, ‘ Brahman’ is the impersonal Eternal Absolute One God having no beginning and no end.   ibid, p.204
In the Yoruba religion, followed by over 10 million people in West Africa (mainly Nigeria), there is One Supreme God, Olorius/Olodumare (The Lord of the Heavens). Nevertheless, modern Yoruba religion is characterised by a multitude of Orisha worship rites which thus render the religion closer to polytheism.
Wilhelm Schmidt discovered in his studies that he found the primitive cultures at the lowest cultural levels had the purer concepts of God. According to Schmidt we find this form of belief among the Pygmies of central Africa, the south-eastern Australian Aborigines, the native Americas of north-central California, the primitive Algonquians, and to a certain extent the Koryaks and Ainu.
Sameul Zwemer spoke of the monotheistic character of the Bushmen, as well as many peoples of the Arctic cultures which he maintained is “Clear…even to a cursory examination.”   Samuel Zwemer, “The Origin of Religion – By Evolution or by Revelation,” (Trans. Vict. Institute, Volume 67; 1937) p. 189
Denying all of Allaah’s Names and Attributes is denial of Allaah’s Lordship, even if a person verbally acknowledges the existence of Allaah. Everything that exists must be characterised by certain attributes that distinguish it from other things.
iii. Denying the rights that He is entitled to such as claiming that Allaah is one with creation or that the universe is eternal.
This is like the theory of wahdat ul-wujood (unity of existence) perinialism and pantheism. Such a the sufis Ibn Arabi and al-Hallaaj and other extremist sufis .
b. Shirk by affirmation – when one affirms another creator or lord besides Allaah. Certain extreme quasi-Islamic sects fall into this when they consider that their religious leaders can control the universe; and have the power to give life & death.
Tawheed in Uloohiyyah means that acts of worship are directed to Allaah only. Thus, to direct any act of worship to other than Allaah is an example of shirk in Uloohiyyah . Examples of acts of worship that are due only to Allaah are du’aa, prayer, prostration, vows and oaths. Shirk in Uloohiyyah is the most common type of shirk amongst people.
Tawheed al-Asmaa wa’s-Sifaat involves affirming for Allaah the Most beautiful Names and Perfect Attributes. So shirk within this category can take place in a number of ways:
By comparing Allaah to the creation.
By comparing creation to Allaah, when creation is given the Names and Attributes that belong solely to Allaah. So to claim that a certain saint knows everything, or can hear the plea of any worshipper, is in fact shirk is Asmaa wa’s-Sifaat .
c. By deriving the names of idols from Allaah’s names, this was the practice of the Jaahiliyyah Arabs.
The Qur’aan mentions shirk in these three categories, Allaah says,
“ Say, (O Muhammad), “Invoke those you claim (as deities) besides Allaah.” they do not possess an atom’s weight (of ability) in the heavens or on the earth, and they do not have therein any partnership (with Him), nor is there for Him from among them any assistant.”
In the Qur’aan and sunnah , it can be seen that shirk is not all of one level. The Prophet (sallallaahu alayhi wasallam) said, “The matter I fear for you most is minor shirk – riya (showing off).” (Musnad Ahmad)
Major shirk is that of making partners with Allaah. Minor shirk is that which does not expel one from Islaam. Examples are showing off, giving an oath by using a name other than Allaah’s Names (such as swearing “by jove”, by one’s parents, or one’s honour – this exalts an object that is not worthy), and attributing occurrences to creation by saying for example, “were it not for the policeman, we would have been robbed.”
Exaggeration – Going to extremes with regards to pious people and objects. Raising their status and transgressing the bounds. The Prophet said “Beware of extremism, for the people before you were destroyed due to it.” (Musnad Ahmad)
Ibn Qayyim said: “Of the primary causes of idol-worship is the exaggeration of the created. So a person is raised above his actual status until he is worshipped.”
For example, some say “Just like an average person cannot approach a king except through a minister or aide, so too it is not possible for a sinful person’s du’a to be answered until he goes through a Prophet or saint.” Thus, Allaah is compared to a king!? This analogy is in fact a proof against those who try to use it!
3. Comparing pious people to prophets. Some people try to seek “blessings” or “barakah” from ‘saints’ or ‘marabouts’ or ‘pirs’ or ‘shaykhs’. Yet this was a special matter exclusive to the Prophet, the companions did not attempt to seek blessings from Aboo Bakr, ‘Umar or any of the major companions.
4. Comparing the life of dead prophets with the life of the living. The belief that prophets are alive in their graves continuing a life similar to the life of this world drives many people to ask dead prophets (alayhim-salaam) for favours and du’as . The type of life that a prophet enjoys after his death is completely different to the one that we experience in this world, to say that they are the same leads to shirk . There is no evidence that the prophets can hear conversations that take place at their graves.
The only matter that the Prophet (sallallaahu alayhi wassallam) stated reaches him after death is the sending of salutations upon him, for Allaah has assigned special angels to bring him these salaams. Other than that there is no evidence that requests reach him as well, henceforth, none of the companions ever requested any matter from him after his death.