β) The theory under consideration is inadmissible also from the philosophical point of view. A quality does not “flow” or tend to revert to nothingness. On the contrary, its very nature demands that it remain constant until destroyed by its opposite or by some positive cause. It is impossible to conceive a quality that would of itself revert to nothingness without the intervention of a destructive cause. Billuart merely beats the air when he says: “_Potest dici qualitas incompleta habens se per modum passionis transeuntis._”(77) What would Aristotle have said if he had been told of a thing that was half ποιόν and half πάσχειν, and consequently neither the one nor the other? Actual grace is transitory; it passes away with the act which it inspires, and consequently may be said to “flow.” But this very fact proves that it is not a dead quality, but a _modus vitalis supernaturalis_. In the dispensation of His grace, God employs no fluent qualities or non-vital entities, but He Himself is the immediate cause of the supernatural elevation of the human soul and its faculties. St. Thomas is perfectly consistent, therefore, when he defines actual grace as a vital act of the soul.(78) 5. PREVENIENT AND COÖPERATING GRACE.—The vital acts of the soul are either spontaneous impulses or free acts of the will. Grace may precede free-will or coöperate with it. If it precedes the free determination of the will it is called prevenient; if it accompanies (or coincides with) that determination and merely coöperates with the will, it is called coöperating grace. Prevenient grace, regarded as a divine call to penance, is often styled _gratia vocans sive excitans_, and if it is received with a willing heart, _gratia adiuvans_. Both species are distinctly mentioned in Holy Scripture. Cfr. Eph. V, 14: “Wherefore he saith: Rise thou that sleepest, and arise from the dead: and Christ shall enlighten thee.” 2 Tim. I, 9: “Who hath delivered us and called us by his holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the times of the world.” Rom. VIII, 26: “Likewise the Spirit also helpeth our infirmity.” Rom. VIII, 30: “And whom he predestinated, them he also called. And whom he called, them he also justified. And whom he justified, them he also glorified.” Apoc. III, 20: “Behold I stand at the gate and knock. If any man shall hear my voice, and open to me the door, I will come in to him, and will sup with him, and he with me.” St. Augustine says: “Forasmuch as our turning away from God is our own act and deed, and this is [our] depraved will; but that we turn to God, this we cannot do except He rouse and help us, and this is [our] good will,—what have we that we have not received?”(79)