positive (adj.)
early 14c., originally a legal term meaning "formally laid down," from Old French positif (13c.) and directly from Latin positivus "settled by agreement, positive" (opposed to naturalis "natural"), from positus, past participle of ponere "put, place" (see position (n.)).

Sense of "absolute" is from mid-15c. Meaning in philosophy of "dealing only with facts" is from 1590s. Sense broadened to "expressed without qualification" (1590s), then "confident in opinion" (1660s); mathematical use is from 1704; in electricity, 1755. Psychological sense of "concentrating on what is constructive and good" is recorded from 1916.
positive (n.)
1520s, from positive (adj.).