The Greeks, the Huns, the Scythians, the Pathans and the Moguls who occupied the land and controlled the political machinery never ruled the minds of the people, for these political events were like hurricanes or the changes of season, mere phenomena of a natural or physical order which never affected the spiritual integrity of Hindu culture. If after a passivity of some centuries India is again going to become creative it is mainly on account of this fundamental unity of her progress and civilisation and not for anything that she may borrow from other countries. It is therefore indispensably necessary for all those who wish to appreciate the significance and potentialities of Indian culture that they should properly understand the history of Indian philosophical thought which is the nucleus round which all that is best and highest in India has grown. Much harm has already been done by the circulation of opinions that the culture and philosophy of India was dreamy and abstract. It is therefore very necessary that Indians as well as other peoples should become more and more acquainted with the true characteristics of the past history of Indian thought and form a correct estimate of its special features. But it is not only for the sake of the right understanding of India viii that Indian philosophy should be read, or only as a record of the past thoughts of India. For most of the problems that are still debated in modern philosophical thought occurred in more or less divergent forms to the philosophers of India. Their discussions, difficulties and solutions when properly grasped in connection with the problems of our own times may throw light on the course of the process of the future reconstruction of modern thought. The discovery of the important features of Indian philosophical thought, and a due appreciation of their full significance, may turn out to be as important to modern philosophy as the discovery of Sanskrit has been to the investigation of modern philological researches. It is unfortunate that the task of re-interpretation and re-valuation of Indian thought has not yet been undertaken on a comprehensive scale. Sanskritists also with very few exceptions have neglected this important field of study, for most of these scholars have been interested more in mythology, philology, and history than in philosophy. Much work however has already been done in the way of the publication of a large number of important texts, and translations of some of them have also been attempted. But owing to the presence of many technical terms in advanced Sanskrit philosophical literature, the translations in most cases are hardly intelligible to those who are not familiar with the texts themselves.