To know the truth is fundamental to human nature because man needs it to guide his or her life and work.
Truth in itself is all that is, or to put it simply, all things that exist are true. Therefore, the nature of man is true but he is born without knowledge of the truth which he must discover by the use of Reason and Revelation. In principle, there cannot be any conflict between the truths of faith and the truths of creation discovered by reason because God is the author of both.
This was not however the view of the Middle Ages. In the 13th Century the poor translations of Aristotle along with misleading commentaries by Jewish and Moorish philosophers led to contradict the truths of faith. The main errors propagated stated that 1) What is true in Religion may be false in philosophy and 2) All men have one soul.
So, St. Thomas Aquinas, to bring clarity into the situation obtained an accurate translation of Aristotle with which to refute false commentators of which Averroes was the most prominent. Thomas set out to express Christian doctrine in scientific form, that is to express sound doctrine in a language that was precise, clear and concise, the result of which is the Summa Contra Gentiles and the Summa Theologica, an unsurpassed synthesis of faith and reason. The best way to show his method is to read an article from the Summa Contra Gentiles presented here since most of my readers have never read St. Thomas.
Summa Contra Gentiles:
CHAPTER LXXHow the Same Effect is from God and from a Natural Agent
Some find it difficult to understand how natural effects are attributable at once to God and to a natural agent.
Arg. 1 One action, it seems, cannot proceed from two agents. If then the action, by which a natural effect is produced, proceeds from a natural body, it does not proceed from God.
Arg. 2. When an action can be sufficiently done by one, it is superfluous to have it done by more: we see that nature does not do through two instruments what she can do through one. Since then the divine power is sufficient to produce natural effects, it is superfluous to employ also natural powers for the production of those same effects. Or if the natural power sufficiently produces its own effect, it is superfluous for the divine power to act to the same effect.
Arg. 3. If God produces the whole natural effect, nothing of the effect is left for the natural agent to produce.
Upon consideration, these arguments are not difficult.
Reply 1. The power of the inferior agent depends upon the power of the superior agent, inasmuch as the superior agent gives to the inferior the power whereby it acts, or preserves that power, or applies it to action; as a workman applies a tool to its proper effect, frequently however without giving the tool the form whereby it acts nor preserving it, but merely giving it motion. The action therefore of the inferior agent must proceed from that agent not merely through its own power, but through the power of all superior agents, for it acts in virtue of them all. And as the ultimate and lowest agent acts immediately, so is the power of the prime agent immediate in the production of the effect. For the power of the lowest agent is not competent to produce the effect of itself, but in power of the agent next above it; and the power of that agent is competent in virtue of the agent above it; and thus the power of the highest agent proves to be of itself productive of the effect, as the immediate cause, as we see in the principles of mathematical demonstrations, of which the first principle is immediate. As then it is not absurd for the same action to be produced by an agent and the power of that agent, so neither is it absurd for the same effect to be produced by an inferior agent and by God, by both immediately, although in different manners.
Reply 2. Though a natural thing produces its own effect, it is not superfluous for God to produce it, because the natural thing does not produce it except in the power of God. Nor is it superfluous, while God can of Himself produce all natural effects, for them to be produced by other causes: this is not from the insufficiency of Gods power, but from the immensity of His goodness, whereby He has wished to communicate His likeness to creatures, not only in point of their being, but likewise in point of their being causes of other things (Chap. XXI).
Reply 3. When the same effect is attributed to a natural cause and to the divine power, it is not as though the effect were produced partly by God and partly by the natural agent: but the whole effect is produced by both, though in different ways, as the same effect is attributed wholly to the instrument, and wholly also to the principal agent.
Is Aquinas relevant today?
Some of the assumptions of his day regarding the physical universe such as that the stars were incorruptible is not true but this does not invalidate his metaphysics of natural philosophy. Aquinas makes a clear distinction between creation and change. The sciences of his day and of our own have as their object the changing world (evolution in our day). Creation, on the other hand, means to cause the whole existence of whatever exists."To create is to cause existence, and all things totally dependent on the Creator for the very fact that they are. The Creator does not take nothing and make something out of nothing. Rather, any thing left to itself, holly separate from the cause of its existence, would be absolutely nothing." (William E. Carroll, "Creation, Evolution, and Thomas Aquinas") Further, Aquinas remarks as you can see above that "When the same effect is attributed to a natural cause and to the divine power, it is not as though the effect were produced partly by God and partly by the natural agent: but the whole effect is produced by both, though in different ways, as the same effect is attributed wholly to the instrument, and wholly also to the principal agent. (Summa Contra Gentiles, LXX, Reply 3)
To put it simply, the monarch butterfly feeding on the yellow zinnia is totally the action of the butterfly and totally the action of God who by its power and design sustains it and gives it being.
Without the study of metaphysics science can misinterpret the nature of reality leading to false assumptions and conclusions such as is happening with the evolutionary sciences. Pope Leo XIII in his encyclical "On the Restoration of Christian Philosophy" written in 1879 in which he upheld the validity of Thomistic philosophy had this to say, "Nor will the physical sciences themselves, which are now in such great repute, and by the renown of so many inventions draw such universal admiration to themselves, suffer detriment, but find very great assistance in the restoration of the ancient philosophy. For, the investigation of facts and the contemplation of nature is not alone sufficient for their profitable exercise and advance; but, when facts have been established, it is necessary to rise and apply ourselves to the study of the nature of corporeal things, to inquire into the laws which govern them and the principles whence their order and varied unity and mutual attraction in diversity arise. To such investigations it is wonderful what force and light and aid the Scholastic philosophy, if judiciously taught would bring." (#29)
For the full article by William E. Carroll applying St. Thomas metaphysics to evolution see the article Creation, Evolution, and St. Thomas Aquinas linked.