principal matrixprincipal minorprincipal normalprincipal partprincipal part of a triangleprincipal part of functionprincipal periodprincipal planes of a quadric surfaceprincipal pointprincipal primeprincipal remainderprincipal rootprincipal root of a numberprincipal sectionsprincipal square rootprincipal subspaceprincipal termprincipal unit normalprincipal unknownsprincipal valueprincipal value of an integralprincipal value of argumentprincipal value of integralprincipal value of logarithmprincipal value of logzprincipiaprincipleprinciple of choiceprinciple of completenessprinciple of conditionalityprinciple of conservation of energyprinciple of countingprinciple of deformationprinciple of detailed balanceprinciple of diminishing returnsprinciple of dualityprinciple of duality in a spherical triangleprinciple of economyprinciple of equivalenceprinciple of extensionprinciple of first differenceprinciple of generalizationprinciple of inclusion and exclusionprinciple of inductionprinciple of insufficient reasonprinciple of least actionprinciple of likelihoodprinciple of mathematical inductionprinciple of nested intervalsprinciple of non contradiction