CORPUS CHRISTI, TX (Catholic Online) - Most of us have not heard of the "illative sense," but we all possess it.  "It is a grand word for a common thing," wrote Blessed John Henry Cardinal Newman in his Essay in Aid of a Grammar of Assent.  It is not fatal that we don't know how to define the illative sense, so long as we have it and use it.  We might adapt that famous saying of Thomas à Kempis regarding compunction: we should rather want to have the illative sense than define it, though perhaps best of all would be to be able to both define it and have it.

To have a natural theology, that is, to know that God exists through reason, we need to recruit our illative sense.  The illative sense is what allows us to take our concrete human experiences--whether they be of nature's beauty, of the demands of conscience (the feeling of guilt, the pangs of remorse, the search for forgiveness), of the sense of the contingency of life, of the peaceful joy elicited by the shallow breathing of your sleeping child beside you in bed, of the honor given to a soldier who sacrificed his life for his fellows, of the haunting beauty of the second movement of Schubert's Piano Sonata in A major, of the pathos of G. M. Hopkins' poem "Spring and Fall," of indeed any created good or beautiful thing--and come to the conclusion that there must be a transcendent reality behind it all, ultimately, He whom we call or know as God.

The potential fodder of the illative sense is the whole host of human experiences: desire, truth, perfection, transcendence, contingency, justice, good, hope, joy, beauty, love.  These experiences are the stuff with which the illative sense works.

The word "illative" comes from the Latin word "illatus," which means "brought in" or "carried into."  And so it is that the illative sense brings us into or carries us into faith, sort of like a butler invites us into the master's mansion.  In Aidan Nichols' words, the illative sense is the kind of reason that "gathers up the fragments of experience into a single and unified judgment," and this "heaping together of tiny indications, not on which by itself is conclusive, produces certitude in ordinary human affairs."

Without the illative sense, we would not be open to the transcendent, and therefore never be open to the reality of a God who has revealed himself to us.  Without this preliminary openness to God as a result of reason's illative sense, we would not be able to put our faith in that God who has revealed himself to us.  The illative sense is therefore a preamble to the faith.  It is the prelude to the "reasonable worship" of God, a "reasonable worship" to which St. Paul calls us to (Rom. 12:1) and to which today the Church, in what she calls the New Evangelization, calls us.

In his book An Essay in Aid of a Grammar of Assent, the Blessed John Henry Cardinal Newman expanded on the notion of the illative sense.  He applied it to the human experience of conscience and moral duty to argue to the conclusion, based upon reason alone, that there must be a divine legislator, and hence God. 

As Newman himself put it: "My true informant, my burdened conscience. . . . pronounces without any misgiving that God exists, and it pronounces quite as surely that I am alienated from him . . . . Thus it solves the world's mystery and sees in that mystery only a confirmation of its own original teaching." 

But, as Aidan Nichols argues in his book A Grammar of Consent, the illative sense can be applied to a whole host of human experiences, and not only the internal experience of conscience to arrive at probable conclusions that God exists.

In fact, we may reasonably rely on the experiences of others, Nichols argues, and not only our own.  Nichols warns however that if we are going to rely on the experience of others in a sort of appeal to authority or argumentum ad verecundiam, we ought to make sure that we look toward "persons of outstanding oral and intellectual integrity."

The illative sense is not the sort of narrow reason which is used in the empirical sciences, or mathematics, or logic, or any serious academic or professional discipline--what Newman called "explicit reason," and what the medieval scholastic called ratio. The conclusions yielded by this reason, which are built upon inference and are clearly demonstrable, are solid but rigid, sort of like an iron rod.  They have their place.  But they also have their place.

There is another place and another kind of reason adequate to that other place.  This is the reason Newman called the illative sense.

The illative sense is found in that broader reason which Newman called "implicit reason," and what the medieval scholastic called intellectus.  Implicit reason is almost an ...