An argument below is proposed to conclude to the Catholic faith as the one true faith. The argument begins by establishing the truth of monotheism, then moves to the nature of religion, and then to the truth of Christianity, then to the truth of the Catholic faith. The argument only proposes the bare bones of the truth of each step. The argument then proceeds to show the logic of the Catholic position.

 God either exists or not.
If God does not exist, then atheism is true.
But atheism is false, for God is the necessary being, without which no thing can exist.
Hence theism is true for atheism is false and theism is true of itself.
For God is the necessary being and a denial of which leads to absurdity.

 Hence because theism is true, then either monotheism or polytheism is true.
If polytheism is true, then many necessary beings exist.
Yet the only necessary being is pure act which is one.
Hence polytheism is false.

 If monotheism is true, then there is only one God.
As God is the necessary being, which is being by nature,
then from the nature of being as only one, there is only one necessary being.
Monotheism is true, then there is only one God.

 As monotheism is true, then the one God is all powerful.
For being without limit is being with all perfect without limit.
Power then is a perfection, when in God, without limit.
Hence the one God controls all things.
But to control all things means to control world history.
Hence the one God controls world history.

 If then the one God has revealed some truths to men, then those truths must be contained within history.
The divine truths contained within history must be lived out by the believers in history.
But to live out truths revealed by God is to live in accord with human nature with respect to God.
To live a human life with respect to God is to regulate human life in accord with 1) knowledge of divine truths, and 2) to direct men towards God through free moral action as regulated by natural moral law and divine positive law.

 Therefore to regulate human life with regard to divinely revealed truths is to 1) propose truths of faith as a form of knowledge 2) propose laws to regulate human behaviour, and 3) propose worship of the one true God through which men can give glory to God.
Therefore to account for the nature of man in respect to God, the true religion must contain a creed, code and cult.
The creed is an expression of the truths revealed by God.
The code is an expression of the law whereby men are to obey and attain the ultimate end.
The cult is the institution by which men are to worship God.

 The one true faith will be revealed by God.
Hence God will provide evidence that He has revealed truths to men, through truth and power.
God has provide evidence that He has revealed truths to men, through truth and power through the revelations received by the Patriarchs, Israel and finally through Jesus Christ.
For Christ as the seal of the prophets both claimed and proved that He was God through His perfect life, His perfect teaching, His fulfillment of prophesy and performance of miracles, such as His own resurrection.
As Christ was God, then His religion is the true faith.
Yet the religion of Christianity is divided into many denominations.
But as truth is one, then only one form of Christianity alone can possibly from Christ.
That form of Christianity must have a unity of doctrine, a creed, a law of conduct from Christ and a form of worship from Christ.
That form of Christianity must also have a strong witness throughout church history, for Christ as God controls Church history.

 When Church history is examined there is a strong universal witness to the creeds, law and worship of the Catholic Church, with its apostolic succession, creeds of faith, church laws, and Eucharistic worship.
No other form of Christianity can produce the evidence from church history for the divine establishment and divine protection granted to the Catholic church.
For no other form of Christianity can both 1) trace its origin back to Christ, and 2) show a strong witness in history to the practice of faith throughout all of church history.
Hence the Catholic faith, based upon the work of Christ, with the bishops and Popes in Rome is the one true faith given by God to men.
Objection 1 - the doctrinal content of the Catholic faith is rejected by Protestants. Hence the Catholic faith cannot claim with certitude that the Catholic faith is the one true faith, for the Catholic faith does not have true doctrine.

 Answer - The Catholic faith alone has a strong witness in church history. Hence only the Catholic faith can be considered as the true faith. If the Catholic faith is shown to have one or more doctrinal errors, then the Catholic faith is false, along with all other Christian denominations. But then, it has never been shown that the Catholic faith has errors, regardless of the claims of its opponents.

 Objection 2 - The historical witness to the Catholic faith is not uniform. For there is witness to the presence of Orthodoxy, with its claims to apostolic succession.

 Answer - The historical evidence for Orthodoxy is not evident until after the schism in 1054 AD. Hence the Orthodox cannot make any historical claim to their own particular ecclesiologies, or doctrines (contraception, divorce and remarriage) prior to the schism of 1054 AD. Hence the history of orthodoxy is without historical basis before 1054 AD. Hence only the Catholic faith which has historical witness from the apostles is the one true faith.

 I realise the above argument is incomplete, due to the inability to demonstrate the truths of the Catholic faith as many Catholic apologists have done in the past. Yet the above argument does provide some indication of where a truth seeker may tend toward to find the true faith.

JM