"Why Tagore?", asked a brilliant young mathematician of me recently. He was referring to an article of mine which had singled out Rabindranath Tagore, Mahatma Gandhi, Jawaharlal Nehru and B.R. Ambedkar as the 'builders' of modern India. "I can understand the other three," the mathematician continued: "Their impact on the world we live in is profound and manifest. But why Tagore?"

There are many readers of this newspaper who are better qualified to answer the question. But since it was asked of me, I had to supply the elements of an answer. This, roughly, is what I said: First, I reminded my friend of the range of Tagore's creative genius. No one since Goethe had worked in so many different fields and done original things in most of them. Tagore was a poet, a novelist, a playwright, an essayist, a polemicist, an autobiographer, a letter-writer, a composer, and an artist. He had good days and bad, but at his best he was world-class in every one of these fields. He was also an institution-builder, and a visionary - as both Santiniketan and Sriniketan, in their original shape and conception, bear testimony.

That he was a great and multi-faceted artist might not, of course, qualify Tagore to be ranked with Gandhi, Nehru and Ambedkar. As social reformers, agitators, and office-holders, those other Indians had a more tangible, or at least more obvious, impact on our lives. Hence their elevation to the status of 'nation-builders' could be more easily discerned, and conceded. But, I told my mathematician-friend, there was a second and more substantial reason why Tagore had to join the company, and perhaps also be placed at the top of the list. This is that the 'idea of India' which Gandhi and Nehru came to uphold and avow was profoundly influenced by the teachings (and, in Gandhi's case, chastisements) of the poet.

It was while he was in South Africa that Gandhi had heard of Tagore, and been impressed by what he heard. When he finally returned to India in 1915, he sent his ashram mates to sit at the feet of the poet. Soon afterwards he joined them. In the last week of March, he visited Santiniketan, and had the first of many exchanges with the poet, which ended only with Tagore's death in 1941. As revealed in Sabyasachi Bhattacharya's edition of their letters, The Mahatma and the Poet, their relationship was very close, but also very contentious.

It was Tagore, I told my mathematician-friend, who broadened Gandhi's horizons, turning a narrow nationalist into a broad-minded internationalist. In school and college buildings across India, some famous lines of Gandhi are engraven: "I do not want my house to be walled in on all sides and my windows to be stuffed. I want the cultures of all the lands to be blown about my house as freely as possible. But I refuse to be blown off my feet by any." How many know that these words were the product of a long debate which began with Gandhi as an English-hating chauvinist, but ended with him conceding Tagore's point that we must rejoice in progressive and liberatory ideas regardless of where they come from? How many know that before those three sentences, quoted above, there is a crucial prefatory sentence which always gets left out? That sentence reads: "I hope I am as great a believer in free air as the great Poet."

Gandhi and Nehru would have not thought and acted as they did had it not been for the guidance they received from Tagore.

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Nehru's relations with Tagore were nowhere near as close, nor as contentious. But the politician profoundly admired the poet - why else would he have sent his only child to study at Santiniketan? Tagore's influence was also manifest in the foreign policy of the government of independent India, as in the desire to build bridges with the other civilisations of Asia, and to do so without demonising the West.

Under Tagore's influence, I told my friend, Gandhi and Nehru developed a kind of nationalism unique in the modern world. It was a nationalism that was inclusive, not exclusive; a nationalism that sought not just political liberty for the Nation but equal rights for all its citizens. Where other nationalisms insisted on a homogeneity of attitudes and worldviews, the idea of India respected and even celebrated the linguistic, cultural and religious diversity of its peoples. And it was inclusive outside its borders, prepared to overlook the horrors of colonialism once colonialism had formally ended, to forge new and equal relations with all the countries and peoples of the world.

If Tagore had merely been a 'creative artist', I concluded, then perhaps one would not have found him fit to rank alongside those other builders of modern India. But in fact Gandhi and Nehru would have not thought and acted as they did had it not been for the guidance they received from Tagore. It was his role as guide and preceptor to Gandhi and Nehru that persuaded me that he must be counted, along with those two and with Ambedkar, as the quartet whose work and example stand apart from and above all other Indians of the 20th century.

I have no doubt that my response to my friend's question was inadequate. But why was the question asked at all? This was no ordinary young man, but a scion of a distinguished family of scholars, widely read, cultivated, and public-spirited. Like his father and grandfather before him, the mathematician had turned his back on a glittering academic career in the West to work in India. It is a land he identifies with, and understands (among other things, he speaks three Indian languages). If an Indian of his sensibility had to be convinced of Tagore's greatness, what then of all the others?

I think Bengal in general, and Bengali intellectuals in particular, are to blame here. They have provincialised and parochialised Tagore, turning a thinker of universal reach and significance into a local hero. To be sure, Tagore had a profound influence on Bengali language and literature. But he never saw himself as exclusively a 'Bengali' - he was, from the first, equally a citizen of India and the world. He may have written mostly in Bengali, but the reach of his ideas extended well beyond Bengal.

There are very many fine historians and literary critics in Bengal who know Tagore's work, literally, inside-out. Yet the only scholars I can think of who have written about Tagore's wider significance are E. P. Thompson and Amartya Sen. Neither is, in any sense, a specialist - and this shows. Their writings on the poet are heartfelt as well as superficial. Books on the greatness and relevance of Gandhi, Nehru and Ambedkar pour off the presses - as they should. Like them, Tagore was a thinker whose work continues to speak to the India of today. Why then do we non-Bengalis know so little about him?

"Why Tagore?" asked the young mathematician. My response, summarised above, was doubtless heartfelt as well as superficial. But that the question was asked, and that I had to give such a clumsy and inadequate answer, is proof that despite their love for and knowledge of Tagore, the intellectuals of Bengal have sold him short. I think we now need a few fat books to tell us what Tagore meant, not for Bengal, but for India and the world.