A work containing some general account of the mutual relations of the chief systems is necessary for those who intend to pursue the study of a particular school. This is also necessary for lay readers interested in philosophy and students of Western philosophy who have no inclination or time to specialise in any Indian system, but who are at the same time interested to know what they can about Indian philosophy. In my two books _The Study of Patanjali_ and _Yoga Philosophy in relation to other Indian Systems of Thought_ I have attempted to interpret the Sämkhya and Yoga systems both from their inner point of view and from the point of view of their relation to other Indian systems. The present attempt deals with the important features of these as also of all the other systems and seeks to show some of their inner philosophical relations especially in regard to the history of their development. I have tried to be as faithful to the original texts as I could and have always given the Sanskrit or Pâli technical terms for the help of those who want to make this book a guide ix for further study. To understand something of these terms is indeed essential for anyone who wishes to be sure that he is following the actual course of the thoughts. In Sanskrit treatises the style of argument and methods of treating the different topics are altogether different from what we find in any modern work of philosophy. Materials had therefore to be collected from a large number of works on each system and these have been knit together and given a shape which is likely to be more intelligible to people unacquainted with Sanskritic ways of thought. But at the same time I considered it quite undesirable to put any pressure on Indian thoughts in order to make them appear as European. This will explain much of what might appear quaint to a European reader. But while keeping all the thoughts and expressions of the Indian thinkers I have tried to arrange them in a systematic whole in a manner which appeared to me strictly faithful to their clear indications and suggestions. It is only in very few places that I have translated some of the Indian terms by terms of English philosophy, and this I did because it appeared to me that those were approximately the nearest approach to the Indian sense of the term. In all other places I have tried to choose words which have not been made dangerous by the acquirement of technical senses. This however is difficult, for the words which are used in philosophy always acquire some sort of technical sense. I would therefore request my readers to take those words in an unsophisticated sense and associate them with such meanings as are justified by the passages and contexts in which they are used. Some of what will appear as obscure in any system may I hope be removed if it is re-read with care and attention, for unfamiliarity sometimes stands in the way of right comprehension. But