Difference between a Mushrik and a Kaafir !

Question: “Is every mushrik (one who assocites partners with Allaah) a kaafir (disbeliever), but not every kaafir is a mushrik? Or are they the same?” 

Shaykh al-Albaani (rahimahullaah) answers: 
“This is the established understanding in people’s minds, except few of them. I will explain that with an example: a man bears witness that none has the right to be worshiped but Allaah and that Muhammad (sallAllaahu 'alayhi wa sallam) is the Messenger of Allaah, and he prays, fasts and so on, but he rejects an aayah from the Qur’aan. This (man) has disbelieved or not disbelieved? He has disbelieved. Has he associated partners with Allaah? That which is correct is that he has associated partners with Allaah. Every kaafir is a mushrik and every mushrik is a kaafir; there is absolutely no difference between the two words… 

Whoever disbelieves has associated partners with Allaah, and whoever associates partners with Allaah has disbelieved; there is no confusion about that. The evidence for this is if we remember the conversation of the believer and the disbeliever in Surat ul-Kahf: {And put forward to them the example of two men: unto one of them We had given two gardens of grapes, and We had surrounded both with date-palms; and had put between them green crops (cultivated fields) / Each of those two gardens brought forth its produce, and failed not in the least therein, and We caused a river to gush forth in the midst of them / And he had property (or fruit) and he said to his companion, in the course of mutual talk: ‘I am more than you in wealth and stronger in respect of men’} [Surat ul-Kahf, 18:32-34] – pay attention now – {And he went into his garden while in a state (of pride and disbelief) unjust to himself. He said: ‘I think not that this will ever perish / And I think not the Hour will ever come-} [Surat ul-Kahf, 18:35-36]. According to your wrong understanding, this (man) has disbelieved but not associated partners with Allaah and he (only) denied the Resurrection. He (then) said: {-and if indeed I am brought back to my Lord, (on the Day of Resurrection), I surely shall find better than this when I return to Him’ / His companion said to him during the talk with him-} [Surat ul-Kahf, 18:36-37] {-‘If you see me less than you in wealth, and children, / It may be that my Lord will give me something better than your garden, and will send on it Husbaan (torment, bolt) from the sky, then it will be a barren slippery earth / Or the water thereof (of the gardens) becomes deep-sunken (underground) so that you will never be able to seek it’ / So his fruits were encircled (with ruin). And he remained clapping his hands (with sorrow) over what he had spent upon it, while it was all destroyed on its trellises, and he could only say: ‘Would that I had ascribed no partners to my Lord!’} [Surat ul-Kahf, 18:39-42]

Therefore, when he denied the Resurrection, he associated partners with Allaah. So, whoever disbelieves in something that has come in the Book (Qur’aan) or the Sunnah, then he is (also) a mushrik during his state of disbelief; this is with respect to the Qur’aanic text. So what is the intellectual reason (for this)? The answer is that (Allaah), the Most High, said: {Have you seen him who takes his own lust (vain desires) as his ilah (god)?}[Surat ul-Jaathiyah, 45:23] Therefore, whoever disbelieves with any type of disbelief is (also) a mushrik, because he himself made his logic to be a partner with His Lord, the Blessed and Most High. Thus, do not differentiate between kufr (disbelief) and shirk (associating partners with Allaah)...  

Likewise, another hadeeth (mentions): ‘Whoever swears by other than Allaah has disbelieved’ and ‘whoever swears by other than Allaah has associated partners with Him.' [Saheeh at-Tirmithee #1535]. He has committed kufr, he has committed shirk. He has committed shirk, he has committed kufr. There is no difference between the two words with regard to terminology in the Islamic legislation. With regard to linguistic terminology, there is a difference no doubt, but the Islamic legislation opens our insight, thinking and understanding. Why is everyone who disbelieves in Allaah, the Mighty and Majestic, with any type of disbelief (also) a mushrik? Because he has made his logic to be a partner with His Lord, the Mighty and Majestic.”

[Source: Silsilat Ul-Hudaa Wa Noor – the series of guidance and light]