Summa summae S. Thomae, Tomus II

Sin taken most generally is divided into original sin, which is derived from Adam to posterity through seminal propagation, and personal sin, which is committed by one's own will. Personal sin is subdivided into actual and habitual. Actual sin is an act or omission disconformable to the rules of morals; habitual sin is the stain left in the soul from actual sin. Of original and habitual sin specially below. Now of actual sin.

Actual sin is divided: 1° into mortal and venial ¹. Mortal is said of that which inflicts death upon the soul, depriving it of sanctifying grace, which is the life of the soul in the supernatural order, and turning it simply away from the last end; whence it is, by its very nature, irreparable, and it induces the guilt of eternal punishment. Venial is said of that which, since it does not deprive one of grace and charity, but only diminishes their fervor, nor turns one simply away from the last end, but only retards its attainment, leaves the principle of life and grace; whence it is not irreparable by its nature, nor does it induce the guilt of eternal punishment, but of temporal punishment only. Of both also we shall treat specially below.

2º Actual sin is divided into sin of commission and omission ², of which we have already spoken. Sin of commission is an act disconformable to the rules of morals; it fights against a negative precept. Sin of omission is the privation of an act owed; it fights against an affirmative precept.

3º Actual sin is divided into sin of heart, of mouth, and of deed ³. Yet this division is not always into diverse sins, but sometimes into diverse degrees of the same sin.

4° It is divided into sin of weakness, which arises from vehement passion; sin of ignorance, which arises from vincible ignorance; and sin of malice, which is committed with full liberty and as it were deliberately, without passion or ignorance.

5° Actual sin is one thing simply such, another against the Holy Spirit, which is sin from malice, whereby the special gifts of grace are repelled or assailed, which are effects of divine love, which is attributed to the Holy Spirit. Six are counted, namely: despair, presumption, impenitence, obstinacy, impugning of the truth known, and envy of fraternal grace.

6° Others are capital sins, others arise from them. The capital sins are counted seven, from St. Greg., book XXXI Moral., chapter 31, namely vainglory (some place pride), envy, avarice, anger, lust, gluttony, and sloth.

7° Finally sin is one thing material, another formal, and this in a twofold sense: 1º Material sin is the evil act itself in itself and considered entitatively; formal, the very malice or deformity of that act or omission. 2º Formal sin is said to be the free transgression of the law imputable to the will; material, a transgression of the law not free, and therefore not imputable to the will, such as are transgressions of the law from invincible ignorance.