(from aptus, "fit"), the natural disposition any thing hath to serve for such or such a purpose.—Thus, oil hath an aptitude to burn, and water to extinguish fire.

or APTNESSE, is often used, in speaking of the talents of the mind, for a promptitude, or disposition to learn things with ease and expedition: in which sense aptness amounts to the same with what the Greeks call εὐαστία, bona indoles, and we sometimes docility. Charlton divides aptness into three parts, viz. acuteness, sagacity, and memory.