Thomas Aquinas

“ Further, sorrow is contrary to pleasure. But the effect of pleasure is expansion: the opposite of which is not depression but contraction. Therefore depression should not be reckoned as an effect of sorrow. ”

“ It is likewise evident that in order to learn anything new, we require study and effort with a strong intention, as is clearly stated in Prov. 2:4,5: "If thou shalt seek wisdom as money, and shall dig for her as for a treasure, then shalt thou understand learning" [Vulg: 'the fear of the Lord'] . Consequently if the pain be acute, man is prevented at the time from learning anything: indeed it can be so acute, that, as long as it lasts, a man is unable to give his attention even to that which he knew already. ”

“ The reason for this is that the will is the cause of human actions: and consequently when we do something that gives pain, the action must of necessity be weakened in consequence. Secondly, action stands in relation to sorrow, as to its principle and cause: and such action must needs be improved by sorrow: thus the more one sorrows on account of a certain thing, the more one strives to shake off sorrow, provided there is a hope of shaking it off: otherwise no movement or action would result from that sorrow. ”

“ Both pleasure and pain, in so far as they draw upon themselves the soul's intention, hinder the reason from the act of consideration, wherefore it is stated in Ethic. vii, 11 that "in the moment of sexual pleasure, a man cannot understand anything." Nevertheless pain attracts the soul's intention more than pleasure does: thus we observe in natural things that the action of a natural body is more intense in regard to its contrary; for instance, hot water is more accessible to the action of cold, and in consequence freezes harder. ”

“ However a difference is to be observed according to the difference of love that a man has for learning or for considering: because the greater his love, the more will he retain the intention of his mind so as to prevent it from turning entirely to the pain.
Reply to Objection 1: Moderate sorrow, that does not cause the mind to wander, can conduce to the acquisition of learning especially in regard to those things by which a man hopes to be freed from sorrow. And thus, "in the tribulation of murmuring," men are more apt to be taught by God. ”

“ External pain arises from hurt done to the body, so that it involves bodily transmutation more than inward sorrow does: and yet the latter is greater in regard to the formal element of pain, which belongs to the soul. Consequently bodily pain is a greater hindrance to contemplation which requires complete repose, than inward sorrow is. Nevertheless if inward sorrow be very intense, it attracts the intention, so that man is unable to learn anything for the first time: wherefore on account of sorrow Gregory interrupted his commentary on Ezechiel (Hom. xxii in Ezechiel) . ”

“ On the contrary, It is written (Prov. 17:22) : "A joyful mind maketh age flourishing: a sorrowful spirit drieth up the bones": and (Prov. 25:20) : "As a moth doth by a garment, and a worm by the wood: so the sadness of a man consumeth the heart": and (Ecclus. 38:19) : "Of sadness cometh death." ”