Tackling Catholic philosophy and theology

I was in a religious order for 5 years and taught at a seminary for 5 years -- and have many years learning Scripture, Philosophy, and Theology. I don't like the above answers at least not the approach.

Theology is the child of 2 parents: Scripture and Philosophy. Learn from the sources before you go to theology proper, which is quite a mess nowadays.

First you must know that by Jewish and Christian life, there is an approach to God by reason, natural theology, and Scripture says just that, that we can know certain things about God by reason alone

"The existence of God and other like truths about God, which can be known by natural reason, are not articles of faith, but are preambles to the articles; for faith presupposes natural knowledge, even as grace presupposes nature, and perfection supposes something that can be perfected. Nevertheless, there is nothing to prevent a man, who cannot grasp proof, accepting, as a matter of faith, something which in itself is capable of being scientifically known and demonstrated." (Summa Theologiae Ia, 2 ii, ad. 1)

Secondly, you have to know what is of the Faith and what isn't. Many of my students hadn't the foggiest. Remember the Augustinian maxim: in essentials, unity; in doubtful matters, liberty; in all things, charity.

So here are my 3 recommendations so that you will enjoy learning more:

1. This is like the Catholic equivalent of C.S. Lewis's Mere Christianity and Josef Pieper's What Catholics Believe, both built around the Creed. IF you want the same sort of thing but contrasting with Protestantism, try the excellent book Catholicism and Fundamentalism by Karl Keating.

2. Theology and Sanity by Frank Sheed -- see the Amazon reviews.

3. If you want Catholic Philosophy but you want it in the unexceptional mainstream form, not in the internecine fights form, I recommend the following though I am assuming a certain attitude on your part, that you want to deal with what is most important first: God and Philosophy, 2nd ed by Etienne Gilson. From the publisher:

   "In this classic work, the eminent Catholic philosopher Étienne Gilson deals with one of the most important and perplexing metaphysical problems: the relation between our notion of God and demonstrations of his existence. Gilson examines Greek, Christian, and modern philosophy as well as the thinking that has grown out of our age of science in this fundamental analysis of the problem of God."

For a survey of Catholic theology, you'd be better off reading the current Catechism, which summarizes the body of beliefs from basics to the more detailed.

There are foot notes a plenty that can point you to both scripture, and also philosophers/theologians for various tenets.

(Plato) > Aristotle > Irenaeus > Augustine > Aquinas > Ratzinger

That order strikes me as missing out on a great deal, beyond the point that Plato and Aristotle weren't "catholic" although Greek philosophy informed some of Paul's letters, and Greek culture and philosophy in the Eastern Mediterranean region where Christianity arose was pretty wide spread.

Missing steps on the journey include Gregory the Great, Origien, and the Apostle Paul ... just to name a few, beyond various Patristic writings.

It is of course necessary to be well versed in Scripture, since Theology and Scripture are inextricably intertwined¹.

Why do I tell you all that? I spent seven years as a Catechist in the RCIA ministry. This answer is very much experienced based.

Saint Thomas' Aquinas Summa Theologica is certainly a core source of Catholic Theology and teaching, but I also recommend his biblical commentaries in Catena Aurea as it collates Patristic commentary on the Gospels - insights of roughly eighty Church Fathers. Since you seem to be looking for a historical progression, being familiar with patristic insights into theology makes this a strong candidate for your pursuit.

¹ For those not already familiar with Scripture, a good start is to first read the Four Gospels, then the Acts of the Apostles, then Paul's letters, the first three books of the Old Testament, Revelation, and then OT references as they arise.

Read St. Thomas Aquinas, especially his Summa Theologica or his own briefer introductory summary of it, the Compendium Theologiæ.

From Fr. Réginald Garrigou-Lagrange, O.P.'s Essence & Topicality of Thomism pt. 1, §2 "The Excellence of Thomism":

St. Robert Bellarmine similarly speaks of St. Thomas in the introduction of his treatise on the Holy Trinity:

Certainly, if everyone proposes with such order, facility, and brevity to us, as I venture to affirm, that he who diligently studies a few of St. Thomas’s questions finds nothing difficult either in Scriptures, the Councils, or the future Fathers of the Trinity; he will make more all-around progress in two months devoted to the Summa than in several months’ study of the Scriptures and the Fathers.

Pope John XXII also said:

He (St. Thomas) has illuminated the Church more than all the other Doctors; to read his books for a year profits man more than to study the doctrine of others for his whole life.

All good, orthodox, Catholic theology is merely footnotes to the Angelic Doctor. Every pope since the 13^th century has endorsed his work as thoroughly Catholic; see the magisterial endors*m*nts quoted here. His Summa Theologica was even placed on the altar, alongside Holy Scriptures, as an authority at the Council of Trent!