It has nothing to do with the name really, but the being. But Muslims do acknowledge the one God, even if they profess many other errors. First, I think there should be noted the difference between worshiping God in Spirit and in truth, offering Him “true worship,” having supernatural faith, obeying Him, etc., and acknowledging God or worshiping God according to religion (which isn’t a theological virtue; it falls under justice).
St. Thomas defines this virtue in the Summa as “to show reverence to one God under one aspect, namely, as the first principle of the creation and government of things.”
newadvent.org/summa/3081.htm
Can Muslims do this? They certainly worship “God” as First Principle and Supreme Governor of all things, but is it the same God we know? Can one acknowledge the one God without acknowledging the Trinity?
First, faith is required to acknowledge the Trinity. The Trinity cannot be reasoned out, as St. Thomas explains:
St. Thomas:
I answer that, It is impossible to attain to the knowledge of the Trinity by natural reason. For, as above explained (12, 4, 12), man cannot obtain the knowledge of God by natural reason except from creatures. Now creatures lead us to the knowledge of God, as effects do to their cause. Accordingly, by natural reason we can know of God that only which of necessity belongs to Him as the principle of things, and we have cited this fundamental principle in treating of God as above (Question 12, Article 12). Now, the creative power of God is common to the whole Trinity; and hence it belongs to the unity of the essence, and not to the distinction of the persons. Therefore, by natural reason we can know what belongs to the unity of the essence, but not what belongs to the distinction of the persons.
newadvent.org/summa/1032.htm
Therefore, we can know of God, as the Principle of all things, apart from faith, but we can only know of the Trinity with faith since it is a revealed dogma. The First Vatican Council also defined that God can be known from natural reason alone (Dei Filius, Canon 2.1) and St. Paul says, on account of this, those who do not acknowledge God (but worship idols, are atheists, etc.) are without excuse (Rom. 1:20).
Therefore, one can acknowledge the one God and Creator of all things without having faith and acknowledging the Trinity. But do Muslims do this?
How can we say whether or not we are talking about the same thing? It is the essence of the thing that determines what it is. If we acknowledge the same essence, we acknowledge the same thing. What we can say about the essence of God is that it is the same as His existence. This is summed up as “God is” or, in His own words, “I AM” or “I AM who AM.” (Exo. 3:14).
This concept is formally referred to as the “aesity” of God. Essentially, aesity means self-existence. Aesity explains the metaphysical nature of God as a purely self-existent being that exists in complete actuality. God is not a being that is created by another god; neither does God create Himself into existence. Rather, God has always existed as an unchanging, completely actualized being. God has his Being of himself and to himself such that he is absolute being and the very definition of existence (see Acts 17:22-28). Since God’s existence is the same as his essence, it follows that God is existence. (Note: this is not to assert pantheism. All other beings participate in his existence on a contingency and thus do not possess the essence of God. Therefore, no other being can be said to be a god or share a part in the godhead since they exist solely on a contingency.) This concept is at the root of the definition of all of God’s other perfections because if God is absolute being he must logically contain in Himself all perfections of being.
Since God’s essence is existence, if one acknowledges His essence, one can only acknowledge He who exists–it is impossible to acknowledge a completely actualized being that is not the one and only God. Similarly, there cannot exist two of such beings, because then neither would contain in Himself all perfections of being.
The CE article on Essence and Existence explains this:
Catholic Encyclopedia:
-If essence and existence were but one thing, we should be unable to conceive the one without conceiving the other. But we are as a fact able to conceive of essence by itself.
-If there be no real distinction between the two, then the essence is identical with the existence. But in God alone are these identical.
newadvent.org/cathen/05543b.htm
Since Muslims do conceive of God as being completely self-actualized, of being non-contingent, as having aesity (see this Muslim article,
al-islam.org/GodAttributes/need.htm ), then they therefore can only be said to acknowledge the one God who exists and it is to Him that they honor and worship as First Principle and Creator according to the virtue of religion.
I would say therefore that we know God; they know of God. This is the difference between affective and speculative knowledge. St. Thomas makes this distinction in his commentary on John to reconcile Biblical passages where Jesus says one must know Him to know the Father with those where people without faith are said to know or worship God (such as those passages cited above from Acts and Romans). We worship God in Spirit and in Truth and serve Him in supernatural faith and charity, they acknowledge and worship only in a natural way.
This of course does not mean what they claim as His revelation actually is or that their religion dates back farther than it actually does, or that they are justified in everything they do, etc. Whether people do good or horrible things in His name does not change or determine who God is.
See also this article by a well-known Catholic philosophy professor:
edwardfeser.blogspot.com/2015/12/christians-muslims-and-reference-of-god.html
