High Quality Content by WIKIPEDIA articles! In mathematics, Kähler differentials provide a generalization of differential forms to arbitrary commutative rings (or schemes). The idea was introduced by Erich Kähler in the 1930s. It was adopted as standard, in commutative algebra and algebraic geometry, somewhat later, following the need to adapt methods from geometry over the complex numbers, and the free use of calculus methods, to contexts where such methods are not available. Let R and S be commutative rings and :R S a ring homomorphism. For example R could be a field and S could be an algebra over R (such as the coordinate ring of an affine variety).