There are many examples of laws, both ancient and modern, which permitted or commanded, for particular cases, things contrary to the current application of natural precepts. Thus, the Spartans and the Romans ordered the murder of infants who were weakly and of slaves whose master had been killed. Some ancient races encouraged robberies committed beyond the boundaries of the states, and savage tribes have been found who had the practice of putting to death parents who were aged or infirm. 326. The causes of wrong applications of the Natural Law are the following: (a) Some causes are involuntary. Thus, the correct application may be difficult, as when more than one moral principle has to be considered and applied; or, if the case is not difficult, the person who makes the application may be mentally undeveloped, or his mind may be blinded on account of his bad education or environment. Examples: The races who saw no infamy in robbery committed against their neighbors, lived in a wild age when such acts of violence seemed necessary as measures of self-protection. The savage killed his aged parents, because to his untutored mind this seemed an act of mercy. (b) Some causes are voluntary, such as neglect of the truth, vicious habits, etc. Examples: St. Paul blames the pagans for their idolatry, because they had darkened their own minds about God. Pirates and bandits who came to regard violence as necessary for their own defense were responsible for their state of mind, inasmuch as they had chosen a life of crime. 327. Transgression of Natural Law, therefore, is not imputable as formal sin if it is not voluntary. Hence: (a) lack of knowledge excuses, when ignorance is involuntary (e.g., those who have not the use of reason, as infants and the unconscious; children and others mentally undeveloped who cannot grasp the meaning of some precept; educated persons who are unable to get a right solution of some knotty problem of morals, etc.); (b) lack of consent excuses in whole or in part (as when one acts through fear). Art. 3: THE POSITIVE DIVINE LAW (_Summa Theologica_, I-II, qq. 98-108.) 328. Meaning.--The Positive Divine Law is the law added by God to the Natural Law, in order to direct the actions of man to his supernatural End, to assist him to a better observance of the Natural Law, and to perfect that which is wanting in human law. (a) The Last End of man is not natural, but supernatural (see 20), and hence it was necessary that, in addition to the precepts which guide man towards his natural beatitude, there should be added precepts that will guide him towards his supernatural beatitude: “The Law of the Lord gives wisdom to little ones” (Ps. xviii. 8).