Concupiscence is the term for the corrupt, disordered desire or inclination of fallen human nature—the inward propensity to evil, the lust that precedes and gives rise to actual sins. The great question dividing Rome and the Reformation is whether this concupiscence is itself sin, or merely the kindling of sin that becomes sin only when the will consents. Rome teaches that concupiscence, the “tinder” (fomes) of sin remaining even after baptism, is not properly sin in itself, but only an inclination that becomes sinful when entertained and consented to; it is called sin only because it comes from sin and inclines to sin. The Reformers, reading Paul, answered that the disordered desire is itself truly and properly sin, even before consent, because it is contrary to the holy law of God which commands not only right actions but a rightly ordered heart. Paul declares that he had not known lust (concupiscence) to be sin except the law had said, “Thou shalt not covet”—proving that coveting, the inward illicit desire, is forbidden and therefore is sin in itself, apart from any outward act. The tenth commandment governs the desires, not merely the deeds. This is no small dispute: if concupiscence is not sin, then a man may be largely sinless while his heart seethes with illicit longing, and the depth of human corruption is vastly understated. The Reformed doctrine humbles man more deeply and exalts grace more highly, confessing that the very bent of the fallen heart needs forgiveness and renewal.