A new interpretation of a 2,500-year-old Sanskrit text upends millennia of debate and affirms an ancient linguist’s remarkably sophisticated grammatical system. Around 500 BCE, the Indian scholar Pa?ini wrote a treatise on Sanskrit, the A??adhyayi, describing a kind of language machine: an algebraic system of rules for producing grammatically correct word forms. The enormity and elegance of that accomplishment—and the underlying computational methodology—cemented Pa?ini’s place as a founder of linguistics. Even so, centuries of commentators have insisted that there are glitches in the machine’s ability to tackle rule conflict (that is, a situation in which two or more rules are simultaneously applicable) and have responded with complex rules and tools aimed at resolving the issues apparently besetting the ancient system. In one fell swoop, this book renders the overwhelming majority of that work obsolete. Linguist Rishi Rajpopat lays out a novel interpretation of Pa?ini’s grammar, focusing on Pa?ini’s only rule dealing with rule conflict, known as 1.4.2. Pa?ini’s Perfect Rule shows that the A??adhyayi indeed functions like a well-oiled machine, capable of handling challenges without any of the complications introduced by later scholars. Rajpopat thus solves an ancient and important problem in Indology and linguistics that will fascinate anyone interested in how language systems—including those of computer programming—operate. In addition, Pa?ini’s Perfect Rule offers meditations on the history of the early Pa?inian tradition, its philosophy, the relationship between rule conflict and accentuation, and aspects of theoretical phonology. A nontechnical preface lays out key findings and foregrounds the deep history of Sanskrit scholarship. This volume opens new horizons for the study of Sanskrit, inviting seasoned experts and novices alike to behold its majesty.