The Difference Between Kufr and Shirk

Question:
What is the difference between disbelief and associating partners with Allah?

Answer:
The difference lies in meaning; as for the ruling, there is no difference between them. However, in terms of meaning, kufr (disbelief) means denial, specifically the denial of the Creator, Glorified and Exalted is He, such as the disbelief of the atheists and communists. Denial means covering the truth, because the linguistic meaning of kufr is covering, and the expiation of sins means covering them over.
Al-kufur (plural of kufr) refers to things that cover those who dwell in them, such as the covering of villages. Kafur (camphor) is also called that because it covers despair. Kufr means covering, and the disbeliever is named so. Even farmers are called kafirun (disbelievers) because they cover the seeds in the ground. Some of the exegetes said that the intended meaning here is the farmers, because they break the seeds in the ground. So kufr means the concealment of the Lord, Glorified and Exalted is He, and the denial of the universe from the Creator, and the denial of communism and the angels. As for shirk (associating partners with Allah), its meaning is affirming Allah, Glorified and Exalted is He, but associating with Him in worship. One associates with Him in worship. So every mushrik (one who associates partners with Allah) is a kafir (disbeliever), but not every kafir is a mushrik. One may be a murtadd (apostate). The kafir may be a mushrik or a murtadd, whereas the mushrik is both a mushrik and a kafir at the same time. There is a relationship of generality and specificity between them, as the scholars of usul al-fiqh (the principles of jurisprudence) say.
The mushrik affirms the existence of Allah, Glorified and Exalted is He, and affirms His lordship, but he associates with Him in worship. As for the kafir, he denies the existence of Allah, Glorified and Exalted is He.