"ars sine scientia nihil est" -- attributed to Jean Mignot, 14th C.
"art without knowledge is nothing".
Jean Mignot, French architect, was active in the late 14th & early 15th Centuries. Consulted on the Milan cathedral (c. 1399) as it was being built he argued that the building would collapse if completed as planned. His arguments, based on structural measurements and geometric schemes, were rooted in the dictum "ars sine scientia nihil est". While the builders retained their Italian preferences they most likely altered aspects of structure to assure stable vaulting.
Milan Cathedral
Rationale for the dictum: "ars sine scientia nihil est".
"ars" The Latin term "ars" (art) may be viewed as the skill and expertise for practicing a profession. In general the term "art" referred to the practice of making things properly - shoes, buildings, clothes, paintings for the church or whatever. By the 14th Century the theory and practice of constructing masonry vaults had acquired a great deal of sophistication. High Gothic Cathedrals, bathed in light and roofed over with heavy masonry vaults, were subject to the laws of gravity. The theory and practice of proper buttressing and wall construction played a key role in the "art" of building Cathedrals. Regional versions of good practice included refinements based on favored geometric and theological schemes. In order for the project to succeed the architect had to be well versed in both the theory and practice of masonry vaulting.
"scientia" The Latin term "scientia" referred broadly to the accumulated knowledge and theory associated with a profession. A proper "scientia" was required for planning and constructing cathedral vaults with appropriate buttressing. For Jean Mignot this knowledge (scientia) included refinements based on his favored geometric and theological schemes. Apparently his French perspectives did not coincide with Italian regional preferences of the time and controversies arose. Theory and practice could not be separated in Mignot's mind. For medieval scholastics, the practice of an art ( ars) without proper knowledge (scientia) could not exist; the two were inseparable and one without the other would be nihil . . .nothing.
See: "Ars Sine Scientia Nihil Est" Gothic Theory of Architecture at the Cathedral of Milan, James S. Ackerman, The Art Bulletin, Vol. 31, No. 2 (Jun., 1949), pp. 84-111. doi:10.2307/3047224
RV 2005