St. Thomas Aquinas defines curiosity thus: it is inordinate desire for truth or the desire for truth for the wrong reasons. Curiosity is a vice, pure and simple. Thomas Aquinas in the Summa Theologiae draws fom Augustine and Aristotle arguing that curiosity is a vice. Curiosity is the desire to know the truth in order to sin, in order to take pride (in the knowledge of it), when it takes one away from an obligatory study, and is directed at times toward an unlawful study (i.e. superstition, theurgy, the dark arts, etc.) . It is the desire to know the truth about creatures without referring one’s knowledge to its due end, namely, to knowledge of God. It is also the desire to know truth above the capacity of one’s own intellegence. In Q. 167 a. 1 II-II ad 1, Aquinas states, citing Aristotle’s Nicomachean Ethics, Book 10 sections 7-8, that “man’s good consists in knowledge of truth, but not any truth–in perfect knowledge of sovereign truth.” Curiosity is the misuse of the knowledge of truth (ad 1). Curiosity includes the desire to know philosophy “in order to assail the faith,” (ad 3). In article 2, he discusses Augustine, who speaks of “concupiscence of the eyes” in Confessions X 35. Augustine, whom he quotes here, gives the perfect definition of curiosity:
“By this it may more evidently be discerned wherein pleasure and wherein curiosity is the object of the senses; for pleasure seeketh objects beautiful, melodious, fragrant, savory, soft; but curiosity, for trial’s sake, seeketh even the contraries of these, not for the sake of suffering annoyance, but out of the lust of experiment and knowledge.”
Yahya ibn Adi, a Christian Arab (early) medieval philosopher from Iraq, discusses curiosity–albeit indirectly–in his work, The Reformation of Morals, when he discusses the virtue of self-control or, at-taṣawwana (التصونة). He states, “It [i.e, self-control] is to be too high-minded to inquire about what is of concern to ignoble, lowly people,” (and thus to keep away from such people), and not acquiring wealth “by contemptible means” (The Reformation of Morals, 3.4). Yahya ibn Adi, like Thomas Aquinas, who came later, sees a connection between the virtue of self-control, and the inordinate desire for knowledge of truth, as well as the desire to know the truth in order to misuse it. The Reformation of Morals represents an unconventional approach to ethics, to the extent that what in the Nicomachean Ethics (representing the western intellectual tradition) namely, self-control–in Greek, asophronia–refers strictly to the body’s appetite for food, drink, and sex, in Reformation refers primarily to the dissipation of the mind. Nevertheless, between the two accounts of virtue and vice, one finds some agreement, though virtue and vice is expressed differently, namely, as “good and bad moral qualities.” Self-control therefore concerns not being curious.