“I had a eureka moment in Cambridge!” That is Dr Rishi Rajpopat, a 27-year-old PhD student from the University of Cambridge, describing the moment he realised he had cracked a grammatical problem that has stumped many Sanskrit scholars since the 5th Century BC.
Rajpopat made the breakthrough by decoding a rule taught by Pāṇini, known as the father of linguistics, and is now encapsulated in his thesis entitled ‘In Pāṇini We Trust: Discovering the Algorithm for Rule Conflict Resolution in the Astādhyāyī’. According to the university, leading Sanskrit experts have described Rajpopat’s discovery as “revolutionary” and it could now mean that Pāṇini’s grammar can also be taught to computers for the first time.
“Pāṇini had an extraordinary mind and he built a machine unrivalled in human history. He didn’t expect us to add new ideas to his rules. The more we fiddle with Pāṇini's grammar, the more it eludes us,” says Rajpopat.
The 2,500-year-old algorithm decoded by him makes it possible, for the first time, to accurately use Pāṇini’s so-called “language machine”. Dr Rajpopat’s discovery makes it possible to “derive” any Sanskrit word, to construct millions of grammatically correct words, using Pāṇini’s revered language machine, which is widely considered to be one of the greatest intellectual achievements in history.
Pāṇini’s system – 4,000 rules detailed in his renowned work, the Aṣṭādhyāyī, which is thought to have been written around 500 BC – is meant to work like a machine. Feed in the base and suffix of a word and it should turn them into grammatically correct words and sentences through a step-by-step process.
Until now, however, there has been a big problem. Often, two or more of Pāṇini’s rules are simultaneously applicable at the same step leaving scholars to agonise over which one to choose. Solving so-called “rule conflicts”, which affect millions of Sanskrit words including certain forms of “mantra” and “guru”, requires an algorithm. Rajpopat’s research shows that Pāṇini’s so-called language machine is also self-sufficient.
"My student Rishi has cracked it – he has found an extraordinarily elegant solution to a problem which has perplexed scholars for centuries. This discovery will revolutionise the study of Sanskrit at a time when interest in the language is on the rise,” said Professor Vincenzo Vergiani, Sanskrit professor and Rajpopat’s PhD supervisor.
Six months before Rajpopat made his discovery, his supervisor at Cambridge, Professor Vincenzo Vergiani, Professor of Sanskrit, gave him some prescient advice: “If the solution is complicated, you are probably wrong”.
A major implication of Dr Rajpopat’s discovery is that now there is the algorithm that runs Pāṇini's grammar, it could potentially teach this grammar to computers.
"Computer scientists working on Natural Language Processing gave up on rule-based approaches over 50 years ago. So teaching computers how to combine the speaker’s intention with Pāṇini’s rule-based grammar to produce human speech would be a major milestone in the history of human interaction with machines, as well as in India's intellectual history," said Rajpopat.
Sanskrit is an ancient and classical Indo-European language from South Asia. It is the sacred language of Hinduism, but also the medium through which much of India’s greatest science, philosophy, poetry and other secular literature have been communicated for centuries. While only spoken in India by an estimated 25,000 people today, Sanskrit has growing political significance in India, and has influenced many other languages and cultures around the world.
“Some of the most ancient wisdom of India has been produced in Sanskrit and we still don’t fully understand what our ancestors achieved. We’ve often been led to believe that we’re not important, that we haven’t brought enough to the table. I hope this discovery will infuse students in India with confidence, pride, and hope that they too can achieve great things,” adds Rajpopat.
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He was born in a suburb of Mumbai and learnt Sanskrit in high school and Pāṇini's Sanskrit grammar informally from a retired Indian professor at no charge whilst pursuing his Bachelor’s in Economics in Mumbai. Following a Master’s at Oxford, for which he raised money by writing to hundreds of potential donors, Rajpopat started his PhD at St. John’s College, Cambridge in 2017 on full scholarship funded by the Cambridge Trust and the Rajiv Gandhi Foundation.
He was awarded his doctorate in January this year and recently joined the School of Divinity at the University of St Andrews.