Shirk is ascribing a partner to Allah in terms of His Rububiyyah (Lordship), Asma wa Sifaat (Names and Attributes) and Uloohiyyah (Worship). The common type of Shirk is the Shirk in Uloohiyyah, which entails supplicating others along with Allah, or dedicating to them worships such as, offerings, vows, reverence, fear, hope, and devotional love.
Shirk is the gravest of all sins due to the following:

1. It is resembling the creatures with the Creator in terms of the attributes of Divinity , for he who ascribes a partner to Allah; he in effect resembles him with Him (Allah). This is the gravest injustice. Allah says: "Verily, Shirk is gross injustice." [Soorah Luqman (31): 13] Injustice signifies putting a thing in a wrong place. Thus, he who worships other than Allah, he places the worship in a place other than its own, and dedicates it to one who does not deserve it; hence, it is gross injustice.

2. Allah has stated that He does not forgive the one who does now disavow Shirk . He says:
"Surely, Allah will not forgive (the sins of) ascribing partners to Him, but He will forgive whatever is short of that to whoever He wishes." [Soorah an-Nisa (4): 48]

3. Allah has stated that a Mushrik (one who commits Shirk) shall be banned from Jannah (Paradise) and that he shall live in Hell-fire forever. Allah, the Exalted, says: "Surely, whoever ascribes a partner to Allah, Allah shall bar him from Jannah and Hell-fire shall be his abode, and the wrongdoers shall have no helpers." [Soorah al-Maidah (5): 72]

4. Shirk nullifies all good deeds. Allah, the Exalted, says: "Were they to commit Shirk, then the good deeds, which they accomplish, would have been nullified." [Soorah al-Anam (6): 88] And Allah says: "It has been revealed to you and to those before you, if you commit Shirk your good deeds shall be nullified and you shall certainly be of the losers." [Soorah az-Zumar (39): 65]

5. The Shirk is the graves of all major sins. The Messenger of Allah (salallahu alaihe wa-sallam) said: "Shall I inform you about the graves of all major sins?" We (Sahabah) said: "Certainly, O Messenger of Allah." He said: "Ascribing partners to Allah, and disobeying parents."

Ibn al-Qayyim said: "Allah has asserted that the purpose of the creation and the commands is that He should be recognized by His Names and Attributes and be worshiped alone, with no partners ascribed to Him, and that people should maintain justice through which the heavens and the earths were established. Allah, the Exalted, says: "Verily, We sent Our Messengers with clear proofs, and sent down with them the Book and the Balance (justice) that people may establish justice." [Soorah al-Hadid (57): 25]

Allah informed us that He sent the Messengers and revealed the Books for people to establish justice. The greatest form of justice is Tawheed, which is its spearhead and backbone, and Shirk is injustice. Allah says: "Surely, Shirk is the greatest Zulm (wrong) indeed." [Soorah Luqman (31): 13]

Shirk is the gravest form of injustice, and Tawheed is the best form of justice. Hence, whatever opposes this purpose most is considered as the gravest of all major sins. Ibn al-Qayyim went on to say: "And since Shirk in particular opposes that purpose, it is absolutely the gravest of all major sins,… Allah, Glory be to Him, neither accepts a good deed performed by a Mushrik, not an intercession made in his favor. He does not respond to his supplication, or accepts his hope for having it fulfilled. The Mushrik is the most ignorant of Allah for setting a rival from creatures to the One Who created them, which is the worst type of ignorance and the worst type of injustice on the part of the Mushrik. Even though the Mushrik does not wrong his Rabb (Lord) by his Shirk, but in reality he wrongs his own self."

7. Shirk is defaming and derogatory from which Allah declared Himself far removed. He who ascribes a partner to Allah, he in effect asserts to Allah what Allah declares Himself free from, and this is the worst form of opposition and defiance to Allah, the Exalted.

B. The Types of Shirk: Shirk is of two types:

THE FIRST TYPE : Greater Shirk, which constitutes apostasy, and condemns the person who practices it to Hell-Fire, and to live therein eternally if he does not relinquish it before death. Shirk is devoting an act of worship to other than Allah, such as; supplication, vows, offerings that are made to jinn, graves or Shaytaan.

Fear of dead, jinn and Shaytaan that they may harm or sicken him and hope for things from others that only Allah can provide such as fulfilling needs and granting relief as practiced nowadays around tombs that are built on graves of pious people. Allah says: "and they worship, instead of Allah that which neither harm nor profit them, and they say, 'These are our intercessors with Allah.'" [Soorah Yunus (10): 18]

THE SECOND TYPE : Lesser Shirk, which does not constitute apostasy, but defects the Tawheed, and is conducive to greater Shirk. It is of two kinds:

1) The first kind: Obvious Shirk which constitutes of UTTERANCES and ACTIONS.

As for the b>UTTERANCES, such as swearing by other than Allah; the Messenger of Allah (salallahu alaihe wa-sallam) said: "He who swears by other than Allah, commits Kufr, or Shirk." [At-Tirmidhee and others]

Or making a statement such as: "Whatever Allah wills and you will."

This statement was made by a man to the Prophet (salallahu alaihe wa-sallam) who objected his statement saying: "Have you made me a rival to Allah? Say: 'Whatever Allah Alone wills."

Or a statement like this, 'Had it not been for Allah and so and so.'

The correct statements are: "Whatever Allah wills and then you will." Because the participle 'then' denotes sequence as well as delay, thus to signify that the will of the slave is subservient to the will of Allah. Allah says: "And you will do nothing unless Allah, the Rabb of the worlds wills it to be done." [Soorah at-Takwir (81): 29]

As for 'and' it signifies absolute combination and association, it does not necessitate order or sequence. Similar to those statement are: 'I have none to resort to except Allah and you' or, 'This is from the blessings of Allah and your blessings.'

As for ACTIONS, such as wearing a ring or a thread for the purpose of warding-off evil, or wearing talismanic outfit or other items for fear of bad eye, or otherwise, if the person who wears them believes that such things are the means of warding-off evil or bringing relief. In that case, wearing them is considered as lesser Shirk, because Allah does not make things as means of protection. But if he believes that these things themselves ward-off evil, then such belief constitutes a major Shirk because he depends on other than Allah.

2) The second kind: The hidden Shirk pertains to intentions and wills such as acting hypocritically and fame – that is, to do a thing which usually is done as a means for seeking nearness to Allah, but does it only so that people commend him for it; such as performing Salat in a perfect manner, or giving charitable gift to be praised, or raising his voice with the Dhikr (remembrance of Allah) or reciting Qur'aan for people to hear him and praise him. When an act of worship is done in Riya (doing an act of worship in order to make people see it or hear it), it would be nullified. Allah, the Exalted, says: "So let him who hope to meet his Rabb do good deeds without ascribing a partner to Allah in worshipping his Rabb." [Soorah al-Kahf (18): 110]

The Prophet (salallahu alaihe wa-sallam) said: "The thing I fear most that you may commit is the lesser Shirk." They asked: 'O Messenger of Allah, what is the lesser Shirk?' He replied: "Riyaa." [Ahmed and at-Tabaranee]

Under this kind falls doing acts of worship for worldly gains, such as performing Hajj, calling our the Adhan (the call for prayer), leading Salaat for money, fame, etc or acquiring knowledge, or fighting in the cause of Allah for money, fame, etc. The Prophet * said: "May the slave of dinar be degraded, may the slave of dirham be degraded, may slave of garment be degraded, for if he is given, he would be satisfied, and if he is not given he is dissatisfied." [Saheeh al-Bukharee]

Ibn al-Qayyim (rahimahullah) said: "As for Shirk which is pertinent to will and intention, it resembles a sea without coast; very few of those who escape it. He who intends by doing good deeds to please other than Allah, and intends to do a thing not for the sake of coming near to Allah, and requested the reward from other than Allah, commits Shirk in terms of intention.

While sincerity is to dedicate all acts of worship and utterances and intentions sincerely to Allah and this is the genuine Hanifiyyah, the deen of Ibraheem which Allah commands all of his slaves to follow. Allah does not accept any other deen from anyone. It is the essence of Islam, as Allah, the Exalted, says: "And he who wants a deen other than Islam, it shall not be accepted from him, and in the world to come he shall be among the losers." [Soorah Al-Imran (3): 85]

It is the deen of Ibraheem, that Allah saved from evil and only the light-witted turns away from it. The Differences between Greater Shirk and Lesser Shirk .

The following differences between the Greater Shirk and the Lesser Shirk are deduced from the above mentioned:

1. The greater Shirk constitutes apostasy, while the lesser Shirk does not constitute apostasy.

2. The greater Shirk condemns the one who practices it to eternal like in the Fire. Whereas the lesser Shirk does not condemn the one who practices it to eternal life in the Fire if he enters it.