Actual sins are prompted by causes within man (camae peccati actualis intra hominem) and causes outside man (camae peccati actualis extra hominem).
The real cause of actual sins within man is his corrupt nature (corruptio hereditaria), as Scripture declares. Rom. 7, 17: "It is no more I that do it, but sin that dwelleth in me." In particular, Scripture mentions as causes of actual sins: a) the spiritual ignorance which results from hereditary corruption, 1 Tim. 1, 13; Matt. 26, 65. 66, cp. with Acts 3, 17; b) sinful emotions and passions, such as fear (Matt. 14, 30; Mark 14, 66 ff.; Gal. 2, 12), wrath (Luke 9, 54. 55; 4, 28. 29), and the like; however, neither man's ignorance nor his sinful passions excuse the evil deeds which are committed because of them, nor do they remove the sinfulness of such acts, 1 Tim. 1, 15; Luke 22, 62; c) the habitual evil inclination (habitus vitiosus) which is produced and confirmed by repeated sinful acts, Jer. 13, 23; for though the inclination to evil is innate in man, there is also an acquired evil inclination, or a vicious disposition, which has its source in his sinful practises (inclinatio ad malum acquisita; peccatum habituale acquisitum; habitus vitiosus acqusitus). It is self-evident that man is responsible also for the sins that have their source in his vicious habits and practises, Rom. 1, 24-27, and which in moments of sober reflection he may earnestly deplore (e. g., a confirmed drunkard).
As causes of actual sins outside man, Scripture mentions a) the devil, who not only actuates the unregenerate, Eph. 2, 2; 1 Cor. 10, 20, but also seeks to seduce the regenerate into sin, 1 Chron. 21, 1; Luke 22, 31; Matt. 16, 23. How Satan tempts believers to commit actual sins is well illustrated by his temptation of Christ, though he could not prevail against Him, Matt. 4, lff. b) Men who mislead persons to sin by their false teachings, Rom. 16, 17. 18; 2 Tim. 2, 17, by ungodly or immoral words and writings, 1 Cor. 15, 33, and by wicked deeds, 2 Pet. 2, 1-3, are also causes of actual sins.
Though God is in no way the cause of actual sin, or of evil deeds, yet He is the author of evil in the sense of tribulation or affliction, Is. 45, 7. This truth Holy Scripture sets forth for the comfort of all believers who endure trials and chastisements in this life, Acts 14, 22, to the glory of God, 2 Cor. 12, 9, and their own good, Rom. 8, 28.