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On the Feast of Saints Cyprian and Justina in the Latin church. For other legally free ebooks, you may access the List of Free eBooks (Arranged by Title) and the List of Free eBooks (Grouped by Subject).
“[I]t is not called divination, if a man foretells things that happen of necessity, or in the majority of instances, for the like can be foreknown by human reason: nor again if anyone knows other contingent future things, through divine revelation: for then he does not divine, i.e. cause something divine, but rather receives something divine. Then only is a man said to divine, when he usurps to himself, in an undue manner, the foretelling of future events: and this is manifestly a sin.” (Saint Thomas Aquinas, Summa Theologiae, 2a 2ae, q. 95, a1c)
“In things done for the purpose of producing some bodily effect we must consider whether they seem able to produce that effect naturally: for if so it will not be unlawful to do so, since it is lawful to employ natural causes in order to produce their proper effects. But, if they seem unable to produce those effects naturally… they come under the head of ‘compact by tokens entered into with the demons’… [I]f in addition there be employed certain characters, words, or any other vain observances which clearly have no efficacy by nature, it will be superstitious and unlawful.” (Saint Thomas Aquinas, Summa Theologiae, 2a 2ae, q. 96, a2c et ad1)