Oxford English Dictionary, s.v. “variable (n.), sense 1.a,” March 2024. "Mathematics and Physics. A quantity or force which, throughout a mathematical calculation or investigation, is assumed to vary or be capable of varying in value."
Shapiro, Stewart; Kouri Kissel, Teresa (2024), Zalta, Edward N.; Nodelman, Uri (편집), “Classical Logic” Spring 2024판, 《The Stanford Encyclopedia of Philosophy》 (Metaphysics Research Lab, Stanford University), 2024년 9월 1일에 확인함