The Summa Grammatica (Latin for Overview of Grammar; c. AD 1280) or Speculative Grammar (Grammatica Speculativa)[1] was a work by the medieval Modist philosopher John of Dacia.
John calls grammar the "idiom of philosophers" and analyzes the modes using Aristotle's Metaphysics.[1][2] He distinguished the vocal sign from the signifying value, called with the Latin expression ratio significandi.[3]