St. Thomas begins with realities already before us—change, causes, contingent existence, degrees of perfection, and ordered activity—and asks what must ultimately ground them.
The Catechism calls approaches like these “converging and convincing arguments”, not proofs in the natural-science sense. Each road moves from an effect we encounter to a cause that does not borrow its power to be or act.
CCC 31–35
STARTWith creation as experiencedASKWhat makes this possible now?ARRIVEAt first cause and final end
THE QUINQUE VIAE
Via means “way” or “road.”
These are five windows onto the same dependence of creation—not five rival definitions of God.
01
EX MOTU
The road from change
POTENTIALmade actual byACTUAL
We observe change.A seed becomes a tree; what can be becomes what is.
Change is received.What is merely potential cannot actualize itself in the same respect.
Borrowed actuality needs a source.An ordered series of changers cannot explain its own present power to change.
Not: everything changes. Rather: changing things depend on what is already actual.
02
EX CAUSA EFFICIENTI
The road from causes
FIRSTCAUSEEFFECT
Effects have efficient causes.Things bring about real changes in other things.
Nothing causes itself to exist.It would have to exist before it existed.
Derivative causes need a first cause.If every cause only borrows causal power, nothing in the series explains it.
Not: merely the earliest event. Rather: the source sustaining every secondary cause.
03
EX POSSIBILI ET NECESSARIO
The road from contingency
CAN BE+CAN CEASE
depends onNECESSARY
Many things need not exist.They begin, change, pass away, and receive existence.
Contingent being is not self-explanatory.What may not be cannot be the ultimate reason that anything is.
Received existence points beyond itself.Ultimately there must be a necessary being whose existence is not derived.
Not: one more durable thing. Rather: the non-derived source of existence.
04
EX GRADIBUS
The road from participation
FULLNESS
Perfections appear in degrees.Created things are truly—but limitedly—good, true, and noble.
They possess perfection by participation.Their goodness and being are received, bounded, and mixed with limitation.
Participation requires a source.What has perfection in a limited way points to what is its fullness and cause.
Not: “some things are better, so a best object exists.” Rather: received perfection points to unreceived fullness.
05
EX GUBERNATIONE RERUM
The road from finality
ORDERED TO AN END
Nature acts in regular ways.Things without intelligence consistently act toward fitting outcomes.
Regular direction is not sheer accident.To act for an end is to be ordered toward what is not yet attained.
Unknowing things do not set their own ends.Their intelligible directedness ultimately requires intelligence.
Not: “science has not explained this complexity.” Rather: why natural activity is ordered to ends at all.
THE SMALL GLOSSARY
Five words unlock the map.
ACT
A perfection already possessed: what a thing presently is.
POTENCY
A real capacity to become or receive a perfection.
CONTINGENT
That which can exist or fail to exist; its being is received.
NECESSARY
That which does not receive existence from another.
FINALITY
The directedness of an action toward an end or good.
ONE REALITY, SEEN FIVE WAYS
The roads do not stop at five names.
Aquinas’s later questions examine what must be true of this first source. The Five Ways are an entrance to that inquiry, not its final page.
IUnmoved moverIIFirst causeIIINecessary beingIVSource of perfectionVIntelligent governor
“FIRST CAUSE AND FINAL END”ONE GODCCC 34
THE PROPER BOUNDARY
Reason reaches the threshold. Revelation opens the door.
NATURAL REASONCan know
That God exists
That creation depends upon him
That he is first cause and final end
CCC 31–35+DIVINE REVELATIONMakes known
The mystery of the Trinity
The Incarnation of the Son
God’s saving covenant and sacramental life
BENEDICT XVI • 16 JUNE 2010
Aquinas does not reduce God to a conclusion. The Creator is infinitely greater than creation, and the mystery of God exceeds what finite reason can comprehend—even when reason truly knows that he is.
