Avicenna (ibn Sina), Kitāb al-Shifāʾ
Silvia Di Vincenzo, Avicenna, ›The Healing, Logic: Isagoge‹: A New Edition, English Translation and Commentary of the Kitāb al-Madḫal of Avicenna’s Kitāb al-Šifāʾ, Scientia Graeco-Arabica, Volume 21, De Gruyter, 2021. https://doi.org/10.1515/9783110726565
Treatise I, Chapter 3, Section 1 (“Knowledge is attained by acquisition”), Q17, p. 31:
The perfection of man, with respect to the fact that he is a man, possessed of intellect — as it will be explained to you in its place — consists in knowing the truth for the sake of itself and the good for the sake of both doing and acquiring it, and man’s first natural disposition and intuition alone is of little help in this [regard]. Most of what is realized for him from this is only realized by acquisition, and this acquisition is the acquisition of the unknown, and what makes it possible to acquire the unknown is the known. It is therefore necessary for man to start by first knowing how he acquires the unknown from the known, and what the state of known things and their arrangement in themselves are such that they provide knowledge of the unknown, that is, so that, when they are arranged in the mind in the required way and the form of those known things is fixed in the mind in the required arrangement, the mind moves from them to the unknown which is the object of the inquiry, and knows it.1
Treatise I, Chapter 3, Section 3 (“Advantages for those who master the discipline of logic”), Q20, pp. 37-39:
However, even if it is so, the oversights that crop up for whoever masters [this] science, if he masters the discipline and puts it to use, are not like [the oversights] that occur to one who has never learned it. Moreover, if [the master of this science] goes back over one of the actions pertaining to his discipline many times, he will be able to compensate for any inattention, should it occur to him. [This is] because if the master of the discipline spoils his work one or many times, he is [however] able to correct it, unless he is extremely stupid. This being the case, no oversight will affect him in the important topics of his discipline that he is obliged to repeat, even if oversights affect [some] secondary subjects.
A man’s convictions include very important things and some others of secondary importance. The master of the discipline of logic can work to double-check a result with regard to those important topics by methodically going back over his work. Sometimes by those means one reaches a [measure of] security against error, like one who adds up the elements of a single calculation many times out of precaution, until the doubt on the result of the addition disappears.2