Fantasy abandoned by reason produces impossible monsters. United with her, she is the mother of the arts and the origin of their marvels.
Source: Los Caprichos, plate 43 ('El sueno de la razon produce monstruos'), Francisco Goya, 1799 — author's explanatory commentary (Prado manuscript)
This is Goya's own gloss on Capricho No. 43. The manuscript commentaries to Los Caprichos (the Prado set) explain plate 43 with essentially this text: imagination abandoned by reason produces impossible monsters; united with reason it is the mother of the arts and the source of their wonders. The line is Goya's, tied to a specific dated work. Slight variance across English translations ('fantasy'/'imagination', 'marvels'/'wonders') is translation drift, not attribution doubt. Confidence held just below 0.9 because the commentary survives in manuscript and its precise wording varies by edition.