READINGS:—St. Thomas, _Summa Theologica_, 1a 2ae, qu. 110, art. 1; qu. 111, art. 1-5.—J. Scheeben, _Natur und Gnade_, Mainz 1861.—M. Glossner, _Lehre des hl. Thomas vom Wesen der Gnade_, Mainz 1871.—Palmieri, _De Gratia Divina Actuali_, thes. 1-16, Gulpen 1885.—Oswald, _Die Lehre von der Heiligung_, 3rd ed., § 1-3, Paderborn 1885.—S. Schiffini, _De Gratia Divina_, disp. 1, sect. 2; disp. 3, sect. 1-5, Freiburg 1901.—Heinrich-Gutberlet, _Dogmatische Theologie_, Vol. VIII, pp. 3 sqq., Mainz 1897.—B. J. Otten, S. J., _A Manual of the History of Dogmas_, Vol. II, St. Louis 1918, pp. 234 sqq. Chapter II. The Properties Of Actual Grace Actual grace has three essential properties: (1) necessity, (2) gratuity, and (3) universality. The most important of these is necessity. Section 1. The Necessity Of Actual Grace In treating of the necessity of actual grace we must avoid two extremes. The first is that mere nature is absolutely incapable of doing any thing good. This error was held by the early Protestants and the followers of Baius and Jansenius. The second is that nature is able to perform supernatural acts by its own power. This was taught by the Pelagians and Semipelagians. Between these two extremes Catholic theology keeps the golden mean. It defends the capacity of human nature against Protestants and Jansenists, and upholds its incapacity and impotence against Pelagians and Semipelagians. Thus our present Section naturally falls into three Articles. Article 1. The Capacity Of Mere Nature Without Grace The capacity of nature in its own domain may be considered with regard either to the intellect or to the will. *Thesis I: Man is capable by the natural power of his intellect to arrive at a knowledge of God from a consideration of the physical universe.* This proposition embodies an article of faith defined by the Vatican Council: “If any one shall say that the one true God, our Creator and Lord, cannot be certainly known by the natural light of human reason through created things, let him be anathema.”(116) For a formal demonstration of this truth we must refer the reader to our treatise on _God: His Knowability, Essence, and Attributes_, pp. 17 sqq. The argument there given may be supplemented by the following considerations: