Saint Thomas’s architecture, like any other work of art, is best studied by itself as though he created it outright; otherwise a tourist would never get beyond its threshold.  Beginning with the foundation which is God and God’s active presence in His Church, Thomas next built God into the walls and towers of His Church, in the Trinity and its creation of mind and matter in time and space; then finally he filled the Church by uniting mind and matter in man, or man’s soul, giving to humanity a free will that rose, like the fleche, to heaven.  The foundation—­the structure—­the congregation—­ are enough for students of art; his ideas of law, ethics, and politics; his vocabulary, his syllogisms, his arrangement are, like the drawings of Villard de Honnecourt’s sketch-book, curious but not vital.  After the eleventh-century Romanesque Church of Saint Michael came the twelfth-century Transition Church of the Virgin, and all merged and ended at last in the thirteenth-century Gothic Cathedral of the Trinity.  One wants to see the end.

The foundation of the Christian Church should be—­as the simple deist might suppose—­always the same, but Saint Thomas knew better.  His foundation was Norman, not French; it spoke the practical architect who knew the mathematics of his art, and who saw that the foundation laid by Saint Bernard, Saint Victor, Saint Francis, the whole mystical, semi-mystical, Cartesian, Spinozan foundation, past or future, could not bear the weight of the structure to be put on it.  Thomas began by sweeping the ground clear of them.  God must be a concrete thing, not a human thought.  God must be proved by the senses like any other concrete thing; “nihil est in intellectu quin prius fuerit in sensu”; even if Aristotle had not affirmed the law, Thomas would have discovered it.  He admitted at once that God could not be taken for granted.

The admission, as every boy-student of the Latin Quarter knew, was exceedingly bold and dangerous.  The greatest logicians commonly shrank from proving unity by multiplicity.  Thomas was one of the greatest logicians that ever lived; the question had always been at the bottom of theology; he deliberately challenged what every one knew to be an extreme peril.  If his foundation failed, his Church fell.  Many critics have thought that he saw dangers four hundred years ahead.  The time came, about 1650-1700, when Descartes, deserting Saint Thomas, started afresh with the idea of God as a concept, and at once found himself charged with a deity that contained the universe; nor did the Cartesians—­until Spinoza made it clear—­seem able or willing to see that the Church could not accept this deity because the Church required a God who caused the universe.  The two deities destroyed each other.  One was passive; the other active.  Thomas warned Descartes of a logical quicksand which must necessarily swallow up any Church, and which Spinoza explored to the bottom.  Thomas said truly that every true cause must be proved as a cause, not merely as a sequence; otherwise they must end in a universal energy or substance without causality—­a source.