Shaykh Sāliḥ al-Fawzān (حفظه الله) was asked the question: “What is the difference between unbelievers (kuffār) and associationists (mushrikīn)?”
The Shaykh answered:[1]
There are generalities [shared between them] and specifics [unique to each of them]. Shirk is more general than kufr, for every mushrik is a kāfir but not every kāfir is a mushrik. The mushrik worships Allāh and worships other than Him, as for the kāfir, then he rejects the existence of Allāh (جل وعلا) and does not acknowledge Allāh (عز وجل), and nor does he acknowledge a religion from amongst the religions. This is the rejecting kāfir. As for the mushrik, he acknowledges and believes, however, he worships Allaah and worships other than Him, hence he is a mushrik kāfir. Thus, every mushrik is a kāfir, but not every kāfir is a mushrik, since the kāfir can be a mulḥid, jāḥid (atheist, rejecter).
Al-Nawawī (رحمه الله) said: “Shirk and kufr can be applied with the one [and same] meaning, which is disbelief in Allāh, the Exalted. And it can also be separated between them whereby shirk is specific to the worship of idols and others from the creation alongside their acknowledgement of Allāh [as their Lord] such as the disbelievers of Quraysh. Thus, kufr is more broad than shirk.”[2]
The kāfir is the one who denies that He is created, has a Lord and is the recipient of bounties and favours for which gratitude is due. So he conceals this truth and reality and this is the meaning of kufr, to cover and conceal. The mushrik is a worshipper of Allāh and of others alongside Him, so he gives what is due only to Allāh, to other than Him.
Arabic Text:
Footnotes
1. Silsilah Sharḥ al-Rasāʾil (p.239).2. Sharḥ Ṣaḥīḥ Muslim (2/71).