Deriving from the Latin term cardo, the cardinal virtues are the four principle virtues upon which Christian morality rests, and the virtues upon which all other moral virtues hinge. The four virtues are prudence (located in the intellect), justice (the will), temperance (in restraint), and fortitude (also in restraint).
It is a system developed through Greek Socratic thought and, in Christianity, through a theological examination of the eight beatitudes of the Sermon on the Mount through the minds of Ambrose, Augustine, Jerome, and chiefly by the work of Thomas Aquinas.
In general, there are four cardinal virtues, because each moral virtue fulfills the conditions of being well judged, serving the common good, being restrained within measure, and having firmness. Aquinas, the principal architect of this system, derives the four virtues from their objects, the rational good which they seek, and from the faculties of the human person in which they reside.
The four virtues, with faith as a foundation, enable the human person to judge well his actions to contribute to the good of others through charity and hope.