The main strength of this book is in the late Professor Miller's Introduction which is lucid and insightful in identifying and placing Patanjali's Yoga Sutras for the general reader. The weakness is in Miller's use of certain non-yogic and sometimes misleading terms in her translation, usage which stems from her position as an academic of yoga and not a practitioner. Sometimes she translates words that probably should not be translated since there are no real English equivalents--for example, "samadhi" itself. And sometimes she uses what I would consider not the most agreeable English equivalent.
Her use of the word "spirit" in the third aphorism is an example: "When thought ceases, the spirit stands in its true identity as observer to the world." The Sanskrit word she is translating is "drashtri" which is usually "seer" although it can also mean "soul," according to B.K.S. Iyengar. When one reads the next aphorism, "Otherwise, the observer [seer] identifies with the turnings of thought" it becomes clear that the seer is not spirit; indeed "spirit" is a confusing word in this context since it has no clear cognate in the dualistic yoga philosophy. The closest equivalent would be "purusha" but that would be inappropriate since that refers to the entire non-material consciousness (as opposed to "prakriti," which is what is manifested). Perhaps I should simply say that "soul" in yogic philosophy is not the same thing as "spirit."
Another example would be her translation of vairagya in I.15 as "dispassion" which is technically correct but misses the larger meaning of the non-attachment that comes from renunciation, which is the point of the aphorism.
I could also quibble with her use of the word "contemplation" as the equivalent of the Sanskrit "samadhi." But it is really impossible to translate the last three limbs of yoga: dharana, dhyana, and samadhi into English, and the contemporary practice is to simply use the Sanskrit terms themselves. And, at any rate, there is considerable controversy about the experience of these states. Miller follows the established practice of rendering them respectively as concentration, meditation, and contemplation. Yet it is clear that samadhi, especially "nirbija samadhi" or seedless samadhi, is beyond contemplation. Georg Feuerstein actually defines samadhi as "ecstasy."
Another strength of the book is the translation itself--once one puts aside the quibbles about some of the terms and looks at the forest, as it were, of the entire expression. Miller has worked hard to make the text readily accessible to the general reader by using familiar terms in familiar sentence structures. She also groups several related aphorisms together and comments on them as a whole, giving each group a title. For example, aphorisms I.17 - I.22 are labeled, "Ways of Stopping Thought." This organization works well in helping the reader to a good overall understanding of Patanjali with only a first reading. Miller has not simplified the text or dumbed it down in any sense. What she has done is to give the pithy statements a sort of liquidity that makes for easy reading.
Her subtitle: "Discipline of Freedom" is an apt description of Patanjali's yoga in the sense that this yoga employs technique and practice to reach liberation whereas other yogas might employ faith and devotion, selfless service, or knowledge as ways to transcend this earthly existence.
I would recommend that this text be studied in conjunction with Iyengar's Light on the Yoga Sutras of Patanjali (1993) since that book contains a more detailed exposition of Patanjali's text and has more extensive commentaries.
--Dennis Littrell, author of "Yoga: Sacred and Profane (Beyond Hatha Yoga)"