The history of this doctrine of the spark, and of the closely connected word _synteresis_, is interesting. The word "spark" occurs in this connexion as early as Tatian, who says (_Or._ 13): "In the beginning the spirit was a constant companion of the soul, but forsook it because the soul would not follow it; yet it retained, as it were, a spark of its power," etc. See also Tertullian, _De Anima_, 41. The curious word _synteresis_ (often misspelt _sinderesis_), which plays a considerable part in mediæval mystical treatises, occurs first in Jerome (on _Ezech._ i.): "Quartamque ponunt quam Græci vocant [Greek: syntêrêsin], quæ scintilla conscientiæ in Cain quoque pectore non exstinguitur, et qua victi voluptatibus vel furore nos peccare sentimus.... In Scripturis [eam] interdum vocari legimus Spiritum." Cf. Rom. viii. 26; 2 Cor. ii. 11. Then we find it in Alexander of Hales, and in Bonaventura, who (_Itinerare_, c. I) defines it as "apex mentis seu scintilla"; and more precisely (_Breviloquium, Pars_ 2, c. 11): "Benignissimus Deus quadruplex contulit ei adiutorium, scilicet duplex naturæ et duplex gratiæ. Duplicem enim indidit rectitudinem ipsi naturæ, videlicet unam ad recte iudicandum, et hæc est rectitudo conscientiæ, aliam ad recte volendum, et hæc est synteresis, cuius est remurmurare contra malum et stimulare ad bonum." Hermann of Fritslar speaks of it as a power or faculty in the soul, wherein God works immediately, "without means and without intermission." Ruysbroek defines it as the natural will towards good implanted in us all, but weakened by sin. Giseler says: "This spark was created with the soul in all men, and is a clear light in them, and strives in every way against sin, and impels steadily to virtue, and presses ever back to the source from which it sprang." It has, says Lasson, a double meaning in mystical theology, (a) the ground of the soul; (b) the highest ethical faculty. In Thomas Aquinas it is distinguished from "intellectus principiorum," the former being the highest activity of the moral sense, the latter of the intellect. In Gerson, "synteresis" is the highest of the affective faculties, the organ of which is the intelligence (an emanation from the highest intelligence, which is God Himself), and the activity of which is contemplation. Speaking generally, the earlier scholastic mystics regard it as a remnant of the sinless state before the fall, while for Eckhart and his school it is the core of the soul.