Aquinas Explained Simply

Why Read Thomas Aquinas?

For many people, Thomas Aquinas seems intimidating.

His books are massive. His arguments are precise. His language can feel foreign to modern readers.

Yet beneath the technical vocabulary lies something surprisingly simple.

Aquinas was asking the same questions we ask today.

Why does anything exist?

What makes something good?

Why do human beings seek happiness?

Can we know God?

Are faith and reason enemies?

What does it mean to be truly free?

For Aquinas, philosophy was never merely an intellectual exercise.

It was a search for reality. A search for truth. And ultimately, a search for God.

His thought remains influential not because it belongs to the Middle Ages, but because it addresses questions that never go away.

Let’s begin where Aquinas begins:

Existence itself.

Essence and Existence

Consider a tree.

You can describe what it is.

It is a living organism. It has roots, branches, and leaves.

That description tells us its essence. Its nature. Its “whatness.”

But there is another question.

Why does this particular tree exist at all?

Its essence does not explain its existence.

A unicorn has an essence. We can describe what a unicorn would be.

Yet unicorns do not exist.

Existence is something different.

Aquinas observed that in every created thing, essence and existence are distinct.

What a thing is differs from the fact that it is.

Everything around us receives existence.

Nothing explains itself.

This insight leads to one of Aquinas’ most profound conclusions.

If all things receive existence, there must ultimately be a reality that does not receive existence.

A reality whose very nature is existence itself.

This is what Aquinas means by God.

Divine Simplicity

Many people imagine God as the most powerful being in the universe.

Aquinas says this is still thinking too small.

God is not simply the strongest creature.

God is not one being among many.

God is Being Itself.

Unlike creatures, God is not composed of parts.

He is not partly wise and partly powerful.

He does not possess goodness.

He is Goodness Itself.

He does not possess truth.

He is Truth Itself.

He does not possess existence.

He is Existence Itself.

This is what Aquinas means by divine simplicity.

Not that God is simple to understand, but that God is utterly unified.

There is no division, limitation, or dependency within Him.

The closer we come to God, the closer we come to the source of everything that is true, beautiful, and good.

Human Nature

Modern culture often treats human nature as something we invent for ourselves.

Aquinas disagrees.

A knife has a purpose. An acorn has a purpose. A bird has a purpose.

Likewise, human beings have a nature.

We are rational creatures.

We possess intellect and will.

We can know truth. We can choose good or evil. We can love. We can sacrifice. We can seek meaning.

Because we possess a definite nature, there are ways of living that help us flourish and ways of living that damage us.

A fish flourishes in water.

A human being flourishes in truth, virtue, friendship, love, and ultimately God.

To understand human nature is to understand what we were made for.

Natural Law

Many people think morality is merely a matter of opinion.

Aquinas saw things differently.

The universe is not chaos.

It possesses order.

Human beings are part of that order.

Because we have a nature, certain actions help us flourish and others harm us.

Natural law is simply our participation in God’s wisdom through reason.

For example:

Life is good.

Truth is good.

Family is good.

Justice is good.

Friendship is good.

These truths are not arbitrary.

They flow from what human beings are.

Natural law is not a list of rules imposed from outside.

It is a guide to human flourishing, like a map showing the path toward a fulfilled life.

Virtue

Most people focus on actions.

Aquinas focuses on character.

The question is not merely:

What should I do?

The deeper question is:

What kind of person am I becoming?

Every choice shapes us.

Repeated choices become habits.

Good habits become virtues.

Virtues are stable dispositions that help us act well.

The classical virtues are prudence, justice, fortitude, and temperance.

Christianity adds faith, hope, and charity.

Virtue makes goodness easier.

A skilled musician no longer struggles over every note.

A virtuous person no longer struggles over every good action.

Goodness becomes second nature.

The goal of morality is not rule-following.

It is transformation.

Free Will

Modern culture often defines freedom as the ability to do whatever we want.

Aquinas offers a deeper understanding.

Freedom is not the power to choose anything. Freedom is the power to choose what is good.

Imagine a pianist.

The more disciplined she becomes, the more freedom she possesses.

The same principle applies to life.

Sin does not increase freedom.

It diminishes it.

Vice becomes a form of slavery.

Virtue becomes liberation.

True freedom is not the absence of limits.

It is the ability to flourish according to our nature.

Angels

Aquinas believed reality contains more than matter.

Not every creature possesses a body.

Angels are purely spiritual beings.

They possess intellect and will but no physical form.

Because they are not material, they do not learn through the senses as humans do.

Their knowledge is immediate and powerful.

The existence of angels reminds us that reality is richer than what we can measure.

Creation extends beyond the visible universe.

The material world is only part of a much larger reality.

Grace

Human beings are capable of great goodness.

Yet we also experience weakness.

We know what is right and often fail to do it.

Aquinas recognized that human nature has been wounded by sin.

We need more than good advice.

We need healing.

Grace is God’s own life shared with us.

It is not merely divine assistance.

It is a participation in the life of God Himself.

Grace elevates human nature.

It does not destroy it.

Just as sunlight perfects a flower rather than destroying it, grace perfects the human soul.

The Christian life is ultimately impossible without grace.

Because holiness is not something we achieve alone.

It is something God accomplishes within us.

Happiness

Every human action aims at happiness.

Even bad decisions are attempts to find some perceived good.

The problem is that finite things cannot satisfy infinite desire.

Money is good. Success is good. Pleasure is good. Friendship is good.

But none of them completely satisfy the human heart.

Why?

Because we were made for something greater.

For Aquinas, perfect happiness is found only in God.

Every earthly joy points beyond itself.

Every beauty hints at a greater Beauty.

Every truth hints at a greater Truth.

Every act of love hints at Love itself.

Our deepest longing is ultimately a longing for God.

Faith and Reason

One of the greatest myths of modern culture is that faith and reason are opposed.

Aquinas taught the opposite.

Both originate from God.

Reason helps us understand the natural world.

Faith reveals truths beyond reason’s reach.

Reason can discover that God exists.

Faith reveals that God is Father, Son, and Holy Spirit.

Reason and faith therefore work together.

Like two wings lifting the human mind toward truth.

When rightly understood, science and faith are not competitors.

Both are paths toward understanding reality.

The Vision of Aquinas

Aquinas offers something increasingly rare in the modern world.

A unified vision of reality.

A vision in which truth is real, goodness is objective, human life has meaning, freedom has purpose, happiness has a destination, faith and reason work together, and God stands at the foundation of everything.

His philosophy begins with ordinary experience.

But it leads ultimately to extraordinary conclusions.

That existence itself is a gift.

That human beings were created for truth and love.

And that every longing of the human heart finds its fulfillment in God.

More than seven centuries after his death, Thomas Aquinas remains one of the greatest guides for anyone seeking to understand reality.

Because he never lost sight of the most important question:

What is the ultimate source of all truth, goodness, beauty, and being?

His answer was simple.

God.

Sources: Sacred Scripture: Exodus 3:14; Psalm 8; Wisdom 13; Matthew 5–7; John 1; John 14; Romans 1–2; Romans 8; 1 Corinthians 13; James 1. St. Thomas Aquinas, Summa Theologiae I, qq. 2–13; Summa Theologiae I-II, qq. 1–114; Summa Contra Gentiles; De Ente et Essentia; Commentary on the Nicomachean Ethics. Catechism of the Catholic Church §§26–49, 1700–1876, 1954–1960, 1803–1845, 1996–2029, 159. Recommended Reading: Edward Feser, Aquinas: A Beginner’s Guide; Peter Kreeft, Summa of the Summa; Étienne Gilson, The Christian Philosophy of St. Thomas Aquinas; Josef Pieper, The Four Cardinal Virtues; Robert Spitzer, New Proofs for the Existence of God; G.K. Chesterton, Saint Thomas Aquinas: The Dumb Ox.